Biaxially oriented polypropylene film

ABSTRACT

A biaxially stretched polypropylene film of the present invention has high stiffness in the film longitudinal direction and can be manufactured by a conventional longitudinal-transverse sequential biaxial stretching method, since the biaxially stretched polypropylene film comprises a polypropylene which comprises a polypropylene having controlled specific values of a melt strength (MS) and a melt flow rate (MFR) at 230° C. or consists of a polypropylene having controlled specific values of a melt strength (MS) and a melt flow rate (MFR) at 230° C. and/or a Trouton ratio of the polypropylene is controlled at a specific value, moreover, the biaxially stretched polypropylene film contains regulated longitudinal fibrils.

TECHNICAL FIELD

[0001] The present invention relates to a biaxially stretchedpolypropylene film suitable in a variety of use including packaging andindustrial use.

BACKGROUND ART

[0002] Based on the social demand for the reduction of waste andresource, there is an increasing demand for decreasing the filmthickness of materials, particularly the materials for packaging uses.Presently, for example, biaxially stretched polypropylene films having athickness of 20 μm are used as the packaging materials. Most of thebiaxially stretched polypropylene films are manufactured by conventionallongitudinal-transverse sequential biaxial stretching method. Inconventional longitudinal-transverse sequential biaxial stretchingmethod, polymer is melted by an extruder, filtered, extruded from a slitdie, and wound around a metal drum to prepare a cooled and solidifiedunstretched film. The unstretched film is passed between rolls ofdifferent rotating speeds and is stretched in the longitudinaldirection. The film is then fed into a tenter, is stretched in thetransverse direction, is heat-set, cooled, and winded. This process isthe typical process for manufacturing biaxially stretched polypropylenefilms.

[0003] Compared with the above-described biaxially stretchedpolypropylene films having a thickness of 20 μm, a 25% reduction ofwastes and resources can be achieved if the same performance and thesame converting ability can be achieved with biaxially stretchedpolypropylene films having a thickness of 15 μm.

[0004] To achieve this, biaxially stretched polypropylene films must betensilized to decrease the elongation against tension applied during theconverting process. During the converting process, the tension works inthe longitudinal direction of the film. Thus, biaxially stretchedpolypropylene films must be tensilized mainly in the longitudinaldirection.

[0005] In general, the heat shrinkage of polypropylene films tends toincrease as the polypropylene films are tensilized. When the dimensionalstability of the film decreases at high temperatures, the film shrinksduring the converting process such as printing, coating, and laminating,thereby drastically decreasing the commercial value of the film.Accordingly, the heat shrinkage must be comparable to or even lower thanthat of common biaxially stretched polypropylene films.

[0006] Japanese Patent Publication of Examined Application Nos.41-21790, 45-37879, and 49-18628 disclose methods for making filmstensilized in the longitudinal directions whereby the film isre-stretched in the longitudinal direction after it is stretched in thelongitudinal and transverse direction to increase the longitudinalstrength of the film. A drawback of these films tensilized in thelongitudinal direction is their low strength in the transversedirection. To overcome this drawback, Japanese Unexamined PatentApplication Publication No. 56-51329 discloses a method whereby apolypropylene sheet having predetermined melting/recrystallizationtemperatures re-stretched in the longitudinal direction after it hasbeen biaxially stretched.

[0007] However, in conventional longitudinal-transverse sequentialbiaxial stretching method, it has been difficult to obtain filmstensilized in the longitudinal direction. In other words, inconventional longitudinal-transverse sequential biaxial stretchingmethod, the film must be kept at a certain temperature to maintain ahalf-melted state because the oriented crystals produced by longitudinalstretching is stretched by transverse stretching. Since most of thecrystals become oriented in the transverse direction after transversestretching, the resulting biaxially stretched polypropylene film has amarkedly high strength in the transverse direction when compared to thatin the longitudinal direction.

[0008] The microstructure, hereinafter referred to as the “fibrilstructure”, of a common biaxially stretched polypropylene filmmanufactured by a conventional longitudinal-transverse sequentialbiaxial stretching method is observed with an atomic force microscope(AFM). A network structure consisting of fibrils having a diameter ofapproximately 20 nm and being mainly oriented in the transversedirection is observed. The fibrils have a high strength in the lengthdirection, but readily deform in the width direction. This fact isconsidered as the cause of bias of the film strength in the transversedirection.

[0009] Moreover, the methods described in Japanese Patent Publication ofExamined Application No. 41-21790 and Japanese Unexamined PatentApplication Publication No. 56-51329 in which re-stretching in thelongitudinal direction is performed are complex, and require highequipment costs. Moreover, the heat shrinkage is higher than that ofcommon biaxially stretched polypropylene films, which is a problem.

DISCLOSURE OF INVENTION

[0010] An embodiment (first embodiment) of the biaxially stretchedpolypropylene film of the present invention is a biaxially stretchedpolypropylene film comprising a polypropylene which comprises apolypropylene having a melt strength (MS) and a melt flow rate (MFR)measured at 230° C. that satisfies formula (1) below:

log(MS)>−0.61 log(MFR)+0.82   (1)

[0011] Another embodiment (second embodiment) of the biaxially stretchedpolypropylene film of the present invention is a biaxially stretchedpolypropylene film comprising a polypropylene which consists of apolypropylene having a melt strength (MS) and a melt flow rate (MFR)that satisfies formula (2) below:

log(MS)>−0.61 log(MFR)+0.52   (2)

[0012] Another embodiment (third embodiment) of the biaxially stretchedpolypropylene film of the present invention is a biaxially stretchedpolypropylene film comprising a polypropylene which comprises apolypropylene having a Trouton ratio of 30 or more.

[0013] Another embodiment (fourth embodiment) of the biaxially stretchedpolypropylene film of the present invention is a biaxially stretchedpolypropylene film comprising a polypropylene which consists of apolypropylene having a Trouton ratio of 16 or more.

[0014] Another embodiment (fifth embodiment) of the biaxially stretchedpolypropylene film of the present invention is a biaxially stretchedpolypropylene film, wherein, in a 1-μm square area of a surface of thefilm, one side of the area being parallel to the longitudinal direction,at least one longitudinal fibril having a width of at least 40 nm andextending across two sides parallel to the transverse direction ispresent.

[0015] The above-described biaxially stretched polypropylene films ofthe present invention not only are tensilized in the longitudinaldirection but also have low heat shrinkage and excellent filmdimensional stability at high temperatures.

BEST MODE FOR CARRYING OUT THE INVENTION

[0016] A biaxially stretched polypropylene film of a first embodiment ofthe present invention comprising a polypropylene which comprises apolypropylene having a melt strength (MS) and a melt flow rate (MFR)measured at 230° C. that satisfies formula (1) below will now bedescribed:

log(MS)>−0.61 log(MFR)+0.82   (1)

[0017] The first embodiment of the present invention is a biaxiallystretched polypropylene film comprising a polypropylene which comprisesa polypropylene having a melt strength (MS) and a melt flow rate (MFR)measured at 230° C. that satisfies formula (1) below:

log(MS)>−0.61 log(MFR)+0.82   (1)

[0018] This kind of polypropylene is commonly referred to as “high meltstrength (MS) polypropylene (PP), and is hereinafter denoted as“HMS-PP”.

[0019] The melt strength (MS) at 230° C. is measured by the followingprocess. Using a melt tension tester manufactured by Toyo Seiki KogyoCo., Ltd., the polypropylene is heated to 230° C., and the resultingmolten polypropylene is extruded at an extrusion rate of 15 mm/min tomake a strand. The tension of the strand at a take-over rate of 6.5m/min is measured, and this tension is defined as the melt strength(MS). The unit therefor is cN.

[0020] The melt flow rate (MFR) at 230° C. is measured according toJapanese Industrial Standards (JIS) K 6758, whereby a melt flow rate(MFR) under a load of 2.16 kg is measured. The unit therefor is g/10min.

[0021] Because the polypropylene used for the biaxially stretchedpolypropylene film of the present invention comprises the polypropylenewhich comprises the polypropylene that satisfies formula (1), abiaxially stretched polypropylene film having a high strength in thelongitudinal direction, which has previously been difficult tomanufacture by conventional longitudinal-transverse sequential biaxialstretching method, can be manufactured. In other words, thepolypropylene that satisfies formula (1) inhibits thelongitudinally-oriented crystals from reorienting in the transversedirection during transverse stretching.

[0022] Preferable examples of methods for preparing the polypropylenesatisfying formula (1) include a method of blending a polypropylenecontaining high-molecular-weight components in a large amount, a methodof blending polymer or oligomer having a branched structure, a methoddisclosed in Japanese Unexamined Patent Application Publication No.62-121704 in which long-chain branched structures are introduced into apolypropylene molecules, and a method disclosed in Japanese PatentPublication No. 2869606 in which a straight-chain crystallinepolypropylene having a melt strength, an intrinsic viscosity, acrystallizing temperature, and a melting point satisfy a predeterminedrelationship, and a melting point that satisfy a predeterminedrelationship, and the boiling-xylene extraction residual rate within apredetermined range is prepared without introducing long-chain branches.

[0023] The biaxially stretched polypropylene film of the presentinvention especially preferably uses a HMS-PP the melt strength of whichis increased by introducing long-chain branches into polypropylenemolecules. Specific examples of the HMS-PP the melt strength of which isincreased by introducing long-chain branches include HMS-PP (Type name:PF-814, etc.) manufactured by Basell Polyolefins, HMS-PP (Type name:WB130HMS, etc.) manufactured by Borealis, and HMS-PP (Type name: D201,etc.) manufactured by Dow Chemical Company, etc.

[0024] An example of an index indicating the degree of long-chainbranching in the polypropylene is a branching index g represented by theequation below:

g=[η]_(LB)/[η]_(Lin)

[0025] wherein [η]_(LB) is the intrinsic viscosity of the polypropylenehaving a long-chain branch, and [η]_(Lin) is the intrinsic viscosity ofa straight-chain crystalline polypropylene having substantially the sameweight average molecular weight as the polypropylene having thelong-chain branch. The intrinsic viscosity is measured by a publiclyknown method in which a sample dissolved in tetralin is measured at 135°C. The weight average molecular weight is measured by a method presentedby M. L. McConnell in American Laboratory, May 63-75 (1978), i.e.,low-angle laser light scattering photometry.

[0026] The branching index g of the polypropylene which is comprised inthe biaxially stretched polypropylene film of the present invention andsatisfies formula (1) is preferably 0.95 or less, and more preferably,0.9 or less. At a branching index exceeding 0.95, the effect of addingthe polypropylene satisfying formula (1) may be diminished, resulting ininsufficient Young's modulus in the longitudinal direction whenprocessed into a film.

[0027] The melt strength (MS) of the polypropylene, which is comprisedin the biaxially stretched polypropylene film of the present inventionand satisfies formula (1), is preferably in the range of 3 to 100 cN. Ifa MS is less than 3 cN, the Young's modulus in the longitudinaldirection of the resulting film may be insufficient. The Young's modulusin the longitudinal direction tends to increase as the melt strength(MS) becomes larger; however, if a melt strength (MS) exceeds 100 cN,film formability may be degraded. More preferably, the melt strength(MS) of the polypropylene satisfying formula (1) is in the range of 4 to80 cN, more preferably, 5 to 40 cN, and most preferably 5 to 20 cN.

[0028] The content of the polypropylene satisfying the formula (1)comprised in the biaxially stretched polypropylene film of the presentinvention is not restricted. However, the polypropylene content ispreferably 1 to 60 percent by weight. A certain degree of effect can beachieved with a relatively small content. If a polypropylene content isless than 1 percent by weight, the stretchability in the transversedirection may be degraded, and improvements in stiffness in thelongitudinal direction may be small. If a polypropylene content exceeds60 percent by weight, the stretchability in the longitudinal direction,the impact resistance, and the haze of the resulting film may bedegraded. More preferably, the content of the polypropylene satisfyingformula (1) is in the range of 2 to 50 percent by weight, andfurthermore preferably, 3 to 40 percent by weight.

[0029] A second embodiment of the present invention is a biaxiallystretched polypropylene film comprising a polypropylene which consistsof a polypropylene having a melt strength (MS) and a melt flow rate(MFR) that satisfies formula (2):

log(MS)>−0.61 log(MFR)+0.52   (2)

[0030] Since the polypropylene used in the biaxially stretchedpolypropylene film of the present invention comprises a polypropylenewhich consists of a polypropylene that satisfies the following formula(2), a biaxially stretched polypropylene film having high stiffness inthe longitudinal direction, which has previously been difficult tomanufacture by conventional longitudinal-transverse sequential biaxialstretching method, can be manufactured.

[0031] The polypropylene used in the present invention preferablysatisfies formula (3), and more preferably satisfies formula (4). Suchpolypropylenes can be made by adjusting the HMS-PP content, for example.The stiffness in the longitudinal direction can be further improved.

log(MS)>−0.61 log(MFR)+0.56   (3)

log(MS)>−0.61 log(MFR)+0.62   (4)

[0032] For example, the polypropylene satisfying formula (2) above canbe prepared by blending a high-melt-strength polypropylene (HMS-PP) witha common polypropylene, and by introducing long-chain branch componentsinto main-chain of the common polypropylene by means of copolymerizationor graft polymerization, so as to increase the melt strength (MS) of thepolypropylene. By blending the HMS-PP, the longitudinally orientedcrystals are prevented from being re-oriented in the transversedirection during transverse stretching.

[0033] In the first and second embodiments of the present invention, themelt flow rate (MFR) of the polypropylene used in the biaxiallystretched polypropylene film is preferably in the range of 1 to 30 g/10min from the point of view of the film formability. At a melt flow rate(MFR) less than 1 g/10 min, problems such as an increase in filtrationpressure during melt extrusion and an increase in time required forreplacing extrusion materials may occur. If a melt flow rate (MFR)exceeds 30 g /10 min, the thickness irregularity in the resulting filmmay be large, which is a problem. The melt flow rate (MFR) is morepreferably 1 to 20 g/10 min.

[0034] In the first and second embodiments of the present invention, themeso pentad fraction (mmmm) of the polypropylene in the biaxiallystretched polypropylene film is preferably in 90 to 99.5%, and morepreferably, 94 to 99.5%. Here, the meso pentad fraction (mmmm) is theindex that directly indicates the conformation of isotacticstereo-regularity in polypropylene.

[0035] Since a film having a superior dimensional stability, heatresistance, stiffness, moisture-proof property, and chemical resistancecan be reliably manufactured by being the meso pentad fraction (mmmm)between 90 to 99.5%, the film that exhibits high converting abilityduring film converting such as printing, coating, metallization,bag-making, and laminating can be manufactured. If a meso pentadfraction (mmmm) is less than 90%, the resulting film tends to exhibit aless stiffness and a large heat shrinkage, as the result, the convertingability during printing, coating, metallization, bag-making, andlaminating may be degraded, and the water vapor permeability may beincreased. If a meso pentad fraction (mmmm) exceeds 99.5%, the filmformability may be degraded. More preferably, the meso pentad fraction(mmmm) is 95 to 99%, and most preferably, 96 to 98.5%.

[0036] In the first and second embodiments of the present invention, theisotactic index (II) of the polypropylene used in the biaxiallystretched polypropylene film is preferably in the range of 92 to 99.8%.If an isotactic index (II) is less than 92%, problems may arise such asless stiffness, large heat shrinkage, and degraded moisture-proofproperty. If an isotactic index (II) exceeds 99.8%, the film formabilitymay be degraded. The isotactic index (II) is more preferably in therange of 94 to 99.5%.

[0037] The polypropylene used in the biaxially stretched polypropylenefilm of the first and second embodiments of the present invention may beblended with scrapped films produced during manufacture of the biaxiallystretched polypropylene film of the present invention or scrapped filmsproduced during manufacture of other types of film or other types ofresins mainly to improve economical efficiency as long as thecharacteristics of the present invention are not degraded.

[0038] The polypropylene used in the biaxially stretched polypropylenefilms of the first and second embodiments of the present inventionmainly comprises homopolymers of the propylene. The polypropylene may bea polymer in which monomer components of other unsaturated hydrocarbonsare copolymerized or may be blended with polymers in which propylene iscopolymerized with monomer components other than propylene, as long asthe purpose of the present invention can be achieved. Examples of thecopolymer components and monomer components for preparing the blendedmaterial include ethylene, propylene (for preparing the copolymerizedblended material), 1-butene, 1-pentene,3-methylpentene-1,3-methylbutene-1,1-hexene,4-methypenten-1,5-ethylhexene-1,1-octene, 1-decene, 1-dodecene,vinylcyclohexene, styrene, allylbenzene, cyclopentene, norbornene, and5-methyl-2-norbornene, etc.

[0039] The above-described characteristic values of the polypropylenesuch as the melt strength (MS), the melt flow rate (MFR), the g value,the meso pentad fraction (mmmm), and the isotactic index (II) arepreferably measured using raw material chips before film-formation.Alternatively, after film-formation, the film may be subjected toextraction with n-heptane at 60° C. or less for approximately 2 hours toremove impurities and additives and then vacuum-dried at 130° C. for atleast 2 hours to prepare a sample. The above-described values may bemeasured using this sample.

[0040] Next, a biaxially stretched polypropylene film comprising apolypropylene which comprises a polypropylene having a Trouton ratio of30 or more is described as a third embodiment of the present invention.

[0041] The third embodiment of the present invention is a biaxiallystretched polypropylene film comprising a polypropylene which comprisesa polypropylene having a Trouton ratio of 30 or more.

[0042] The Trouton ratio is measured by a converging flow methodaccording to a theory by Cogswell [Polymer Engineering Science, 12, 64(1972)]. The Trouton ratio is a ratio of the extensional viscosity toshear viscosity at 230° C. and a strain rate of 60 S⁻¹ calculated froman extensional viscosity-extensional strain rate curve and a shearviscosity-shear strain rate curve approximated by an exponentialfunction.

[0043] Since the biaxially stretched polypropylene film of the thirdembodiment of the present invention comprises a polypropylene whichcomprises a polypropylene having a Trouton ratio of 30 or more, abiaxially stretched polypropylene film having high stiffness in thelongitudinal direction, which has previously been difficult tomanufacture by a conventional longitudinal-transverse sequential biaxialstretching method, can be manufactured. Namely, the polypropylene havinga Trouton ratio of 30 or more prevents the longitudinally orientedcrystals from re-orienting in the transverse direction during transversestretching.

[0044] The Trouton ratio of the polypropylene comprised in the biaxiallystretched polypropylene film of the present invention is preferablyhigh. However, at an excessively high ratio, the film formability andsurface haze may be degraded. The Trouton ratio of the polypropylenecomprised in the biaxially stretched polypropylene film of the presentinvention is more preferably 35 or more, and furthermore preferably inthe range of 40 to 100.

[0045] Preferable examples of methods for preparing a polypropylenehaving a Trouton ratio of 30 or more include a method of blending apolypropylene containing high-molecular-weight components in a largeamount, a method of blending polymer or oligomer having a branchedstructure, a method disclosed in Japanese Unexamined Patent ApplicationPublication No. 62-121704 in which long-chain branched structures areintroduced into polypropylene molecules, and a method disclosed inJapanese Patent Publication No. 2869606 in which a straight-chaincrystalline polypropylene having a melt strength, an intrinsicviscosity, a crystallizing temperature, and a melting point that satisfya predetermined relationship, and the boiling-xylene extraction residualrate within a predetermined range is prepared without introducing oflong-chain branches, which are the methods of increasing the meltstrength (MS) of the polypropylene.

[0046] Among these high melt strength polypropylene (HMS-PP) describedabove, the biaxially stretched polypropylene film of the thirdembodiment of the present invention preferably comprises a HMS-PP whichhas the increased melt strength by introducing long-chain branches intopolypropylene molecules. Specific examples of the HMS-PP which has theincreased melt strength by introducing a long-chain branch includeHMS-PP (Type name: PF-814, etc.) manufactured by Basell Polyolefins,HMS-PP (Type name: WB130HMS, etc.) manufactured by Borealis, and HMS-PP(Type name: D201, etc.) manufactured by Dow Chemical Company, etc.

[0047] An example of an index indicating the degree of long-chainbranching in the polypropylene is a branching index g represented by theequation below:

g=[η]_(LB)/[η]_(Lin)

[0048] wherein [η]_(LB) is the intrinsic viscosity of the polypropylenehaving a long-chain branch, and [η]_(Lin) is the intrinsic viscosity ofa straight-chain crystalline polypropylene having substantially the sameweight average molecular weight as the polypropylene having thelong-chain branch. The intrinsic viscosity is measured by a publiclyknown method in which a sample dissolved in tetralin is measured at 135°C. The weight average molecular weight is measured by a method presentedby M. L. McConnell in American Laboratory, May 63-75 (1978), i.e.,low-angle laser light scattering photometry.

[0049] The branching index g of the polypropylene which is comprised inthe biaxially stretched polypropylene film of the third embodiment ofthe present invention and has a Trouton ratio of 30 or more ispreferably 0.95 or less, and more preferably, 0.9 or less. If abranching index exceeds 0.95, the effect of adding the HMS-PP may bediminished, resulting in insufficient Young's modulus in thelongitudinal direction when processed into a film. More preferably, thebranching index g is 0.9 or less.

[0050] The melt strength (MS) of the polypropylene which is comprised inthe biaxially stretched polypropylene film of the third embodiment ofthe present invention and has a Trouton ratio of 30 or more ispreferably in the range of 3 to 100 cN. If a melt strength (MS) is lessthan 3 cN, the Young's modulus in the longitudinal direction of theresulting film may be insufficient. The Young's modulus in thelongitudinal direction tends to increase as the melt strength (MS)becomes larger; however, at a melt strength (MS) exceeding 100 cN, filmformability may be degraded. More preferably, the melt strength ofHMS-PP is in the range of 4 to 80 cN, more preferably, 5 to 40 cN, andfurthermore preferably 5 to 20 cN.

[0051] The content of the polypropylene having a Trouton ratio of 30 ormore comprised in the biaxially stretched polypropylene film of thethird embodiment of the present invention is not restricted. However,the content of the polypropylene having a Trouton ratio of 30 or more ispreferably 1 to 60 percent by weight. A certain degree of effect can beachieved with a relatively small content. When the content of thepolypropylene having a Trouton ratio of 30 or more is less than 1percent by weight, the stretchability in the transverse direction may bedegraded, and improvements in stiffness in the longitudinal directionmay be small. When the content of the polypropylene having a Troutonratio of 30 or more exceeds 60 percent by weight, the stretchability inthe longitudinal direction, the impact resistance, and the haze may bedegraded. More preferably, the content of the polypropylene having aTrouton ratio of 30 or more is in the range of 2 to 50 percent byweight, and furthermore preferably, 3 to 40 percent by weight.

[0052] A fourth embodiment of the present invention is a biaxiallystretched polypropylene film comprising a polypropylene which consistsof a polypropylene having a Trouton ratio of 16 or more.

[0053] Because the biaxially stretched polypropylene film according tothe fourth embodiment of the present invention comprises a polypropylenewhich consists of a polypropylene having a Trouton ratio of 16 or more,a biaxially stretched polypropylene film having high stiffness in thelongitudinal direction, which has previously been difficult tomanufacture by conventional longitudinal-transverse sequential biaxialstretching, can be manufactured.

[0054] The Trouton ratio of the polypropylene used in the biaxiallystretched polypropylene film of the present invention is preferablyhigh. However, at an excessively high ratio, the film formability andthe surface haze may be degraded. The Trouton ratio of the polypropyleneused in the biaxially stretched polypropylene film of the presentinvention is more preferably 18 or more, furthermore preferably in therange of 20 to 50, and most preferably in the range of 20 to 45. TheTrouton ratio can be controlled by adjusting the amount of additiveHMS-PP as described below, and the stiffness in the longitudinaldirection can be further increased.

[0055] Examples of methods for preparing a polypropylene having aTrouton ratio of 16 or more include a method in which ahigh-melt-strength polypropylene (hereinafter, denoted as HMS-PP) havinga high melt strength (MS) described below is blended with a commonpolypropylene and a method in which long-chain branch components areintroduced into the main chain of a common polypropylene by means ofcopolymerization or graft polymerization, so as to increase the meltstrength (MS) of the polypropylene. With the HMSPP, thelongitudinally-oriented crystals are prevented from re-orienting in thetransverse direction during the transverse stretching.

[0056] The types of polypropylene used in the biaxially stretchedpolypropylene film of the fourth embodiment of the present invention arenot restricted as long as the Trouton ratio is 16 or more. For example,a polypropylene having following properties is preferably comprised.

[0057] The polypropylene preferably comprises a polypropylene having aTrouton ratio of 30 or more so as to achieve a Trouton ratio of 16 ormore. Examples of methods for preparing a polypropylene having a Troutonratio of 30 or more include a method in which a high-melt-strengthpolypropylene (hereinafter, HMS-PP) having a high melt strength (MS) isblended with a common polypropylene and a method in which long-chainbranch components are introduced into the main chains of a commonpolypropylene by means of copolymerization or graft polymerization, soas to increase the melt strength (MS) of the polypropylene. With theHMSPP, the longitudinally-oriented crystals are prevented fromre-orienting in the transverse direction during the transversestretching.

[0058] In the third and fourth embodiments of the present invention, themelt flow rate (MFR) of the polypropylene used in the biaxiallystretched polypropylene film is preferably in the range of 1 to 30 g/10min from the point of view of the film formability. If a melt flow rate(MFR) is less than 1 g/10 min, problems such as an increase infiltration pressure during melt extrusion and an increase in timerequired for replacing extrusion materials may occur. If a melt flowrate (MFR) exceeds 30 g /10 min, the thickness irregularity in theresulting film may be large, which is a problem. The melt flow rate(MFR) is more preferably 1 to 20 g/10 min.

[0059] In the third and fourth embodiments of the present invention, themeso pentad fraction (mmmm) of the polypropylene used in the biaxiallystretched polypropylene film is preferably in 90 to 99.5%, and morepreferably, 94 to 99.5%. Here, the meso pentad fraction (mmmm) is theindex that directly indicates the conformation of isotacticstereo-regularity in polypropylene. If a meso pentad fraction (mmmm) is90 to 99.5%, a film having superior dimensional stability, heatresistance, stiffness, moisture-proof property, and chemical resistancecan be reliably manufactured. Thus, a film that exhibits high convertingability during film converting processes such as printing, coating,metallization, bag-making, and laminating can be manufactured. If a mesopentad fraction (mmmm) is less than 90%, the resulting film tends toexhibit a less stiffness and a large heat shrinkage, which may result indegradation in converting ability during printing, coating,metallization, bag-making, and laminating, and in an increase in highwater vapor permeability. If a meso pentad fraction (mmmm) exceeds99.5%, the film formability may be degraded. More preferably, the mesopentad fraction (mmmm) is 95 to 99%, and most preferably, 96 to 98.5%.

[0060] In the third and fourth embodiments of the present invention, theisotactic index (II) of the polypropylene used in the biaxiallystretched polypropylene film is preferably in the range of 92 to 99.8%.If an isotactic index (II) is less than 92%, the resulting film mayexhibit a less stiffness, a large heat shrinkage, and may have adegraded moisture-proof property, which are problems. If an isotacticindex (II) exceeds 99.8%, the film formability may be degraded. Theisotactic index (II) is more preferably in the range of 94 to 99.5%.

[0061] The polypropylene used in the biaxially stretched polypropylenefilm of the third and fourth embodiments of the present invention may beblended with scrapped films produced during manufacture of the biaxiallystretched polypropylene film of the present invention or scrapped filmsproduced during manufacture of other types of film or other types ofresins to improve economical efficiency as long as the characteristicsof the present invention are not degraded.

[0062] The polypropylene used in the biaxially stretched polypropylenefilm of the third and fourth embodiments of the present invention mainlycomprises homopolymers of the propylene. The polypropylene may be apolymer in which monomer components of other unsaturated hydrocarbonsare copolymerized or may be blended with a polymer, which is prepared bycopolymerizing a propylene with a monomer component other thanpropylene, as long as the purpose of the present invention can beachieved. Examples of the copolymer components and monomer componentsfor preparing the blended material include ethylene, propylene (forpreparing the copolymerized blended material), 1-butene, 1-pentene,3-methylpentene-1,3-methylbutene-1,1-hexene,4-methypentene-1,5-ethylhexene-1,1-octene, 1-decene, 1-dodecene,vinylcyclohexene, styrene, allylbenzene, cyclopentene, norbornene, and5-methyl-2-norbornene, etc.

[0063] The above-described characteristic values of the polypropylenesuch as the Trouton ratio, the melt strength (MS), the melt flow rate(MFR), the g value, the meso pentad fraction (mmmm), and the isotacticindex (II) are preferably measured using raw material chips beforefilm-formation. Alternatively, after film-formation, the film may besubjected to extraction with n-heptane at 60° C. or less forapproximately 2 hours to remove impurities and additives and thenvacuum-dried at 130° C. for at least 2 hours to prepare a sample. Theabove-described values may be measured using this sample.

[0064] In order to increase the strength and improve the filmformability, at least one additive that has compatibility with thepolypropylene and can provide plasticity during stretching is comprisedin the biaxially stretched polypropylene films of the first, second,third, and fourth embodiments of the present invention. Here, theadditive that can provide plasticity refers to a plasticizer thatenables stable stretching to a high stretching ratio. Without theadditive, the purpose of the present invention is not sufficientlyachieved, and the film formability is degraded. The additive ispreferably at least one of petroleum resin substantially containing nopolar group and/or terpene resin substantially containing no polar groupfrom the point of view of achieving stretching to a high stretchingratio and improving barrier property.

[0065] The petroleum resin substantially containing no polar grouprefers to a petroleum resin containing no polar groups such as hydroxyl,carboxyl, halogen, or sulfone, or modified forms thereof, etc. Specificexamples of the resin are cyclopentadiene resins made from petroleumunsaturated hydrocarbon and resins containing higher olefin hydrocarbonas the primary component.

[0066] Preferably, the glass transition temperature (hereinafter,sometimes referred to as Tg) of the petroleum resin substantiallycontaining no polar group is 60° C. or more. If a glass transitiontemperature (Tg) is less than 60° C., the effect of improving thestiffness may be small.

[0067] Particularly preferably, a hydrogen-added (hereinafter, sometimesreferred to as hydrogenated) petroleum resin, whose hydrogenation rateis 90% or more and more preferably 99% or more, is used. Arepresentative example of the hydrogen-added petroleum resin is analicyclic petroleum resin such as polydicyclopentadiene having a glasstransition temperature (Tg) of 70° C. or more and a hydrogenation rateof 99% or more.

[0068] Examples of the terpene resin substantially containing no polargroup are terpene resins containing no polar group such as hydroxyl,aldehyde, ketone, carboxyl, halogen, or sulfone, or the modified formsthereof, etc., i.e., hydrocarbons represented by (C₅H₈)n and modifiedcompounds derived therefrom, wherein n is a natural number between 2 and20.

[0069] The terpene resins are sometimes called terpenoids.Representative compounds thereof include pinene, dipentene, carene,myrcene, ocimene, limonene, terpinolene, terpinene, sabinene,tricyclene, bisabolene, zingiberene, santalene, campholene, mirene, andtotarene, etc. In relation to the biaxially stretched polypropylene filmof the present invention, hydrogen is preferably added at hydrogenationrate of 90% or more, particularly preferably, 99% or more. Among them,hydrogenated β-pinene and hydrogenated β-dipentene are particularlypreferred.

[0070] The bromine number of the petroleum resin or the terpene resin ispreferably 10 or less, more preferably 5 or less, and most preferably 1or less.

[0071] The amount of the additive may be large enough to achieve theplasticizing effect. Preferably, the total amount of the petroleum resinand the terpene resin is in the range of 0.1 to 30 percent by weight.When the amount of the additive resins is less than 0.1 percent byweight, the effect of improving the stretchability and the stiffness inthe longitudinal direction may be small and the transparency may bedegraded. When an amount exceeds 30 percent by weight, thermaldimensional stability may be degraded, and the additive may bleed outonto the film surface, resulting in degradation of slipperiness. Theamount of additives or the total amount of the petroleum resin and theterpene resin is more preferably 1 to 20 percent by weight, andfurthermore preferably 2 to 15 percent by weight.

[0072] When a petroleum resin and/or a terpene resin that contain polargroups is used as the additive, voids may readily be formed inside thefilm, the water vapor permeability may increase, and bleeding out ofantistatic agents or lubricants may be prevented due to their poorcompatibility with polypropylene.

[0073] Specific examples of additives that has compatibility with thepolypropylene and can provide plasticizing effect during stretchinginclude “Escorez” (type name: E5300 series, etc.) manufactured by TornexCo., “Clearon” (type name: P-125, etc.) manufactured by YasuharaChemical Co., Ltd., and “Arkon” (type name: P-125, etc.) manufactured byArakawa Chemical Industries, Ltd., etc.

[0074] The biaxially stretched polypropylene film of the first, second,third, and fourth embodiments of the present invention can be made intoa metallized film having a high gas barrier property by depositing ametallization layer on at least one side of the film.

[0075] Moreover, at least one side of the biaxially stretchedpolypropylene film of the first, second, third, and fourth embodimentsof the present invention may be provided with a coating layer composedof polyesterpolyurethane-based resin and a metallization layer. As aresult, a metallized film having a superior gas barrier property to thatof the above-described metallized film can be made.

[0076] In achieving high gas barrier property after metallization, thecoating layer is preferably formed by applying a blended coatingmaterial containing a water-soluble organic solvent and a water-solubleand/or water-dispersible crosslinked polyesterpolyurethane-based resin,and drying the applied coat.

[0077] The polyesterpolyurethane-based resin used in the coating layerincludes polyesterpolyol obtained by esterifying dicarboxylic acid and adiol component, and polyisocyanate. A chain extension agent may beincluded, if necessary.

[0078] Examples of the dicarboxylic acid component in thepolyesterpolyurethane-based resin used in the coating layer includeterephthalic acid, isophthalic acid, 2,6-naphthalene dicarboxylic acid,adipic acid, trimethyladipic acid, sebacic acid, malonic acid,dimethylmalonic acid, succinic acid, glutaric acid, pimelic acid,2,2-dimethylglutaric acid, azelaic acid, fumaric acid, maleic acid,itaconic acid, 1,3-cyclopentane dicarboxylic acid, 1,2-cyclohexanedicarboxylic acid, 1,4-cyclohexane dicarboxylic acid, 1,4-naphthalicacid, diphenic acid, 4,4′-hydroxybenzoic acid, and 2,5-naphthalenedicarboxylic acid, etc.

[0079] Examples of the diol component in the polyesterpolyurethane-basedresin used in the coating layer include aliphatic glycols such asethylene glycol, 1,4-butanediol, diethylene glycol, and triethyleneglycol; aromatic diols such as 1,4-cyclohexane dimethanol; andpoly(oxyalkylene)glycols such as polyethylene glycol, polypropyleneglycol, and polytetramethylene glycol, etc.

[0080] The polyesterpolyurethane-based resin used in the coating layermay be copolymerized with hydroxycarboxylic acid, etc. such as p-hydroxybenzoic acid, etc. in addition to containing the dicarboxylic acidcomponent and the diol component. Moreover, although these have a linearstructure, branching polyester may be made using ester-formingcomponents of trivalent or more.

[0081] Examples of polyisocyanate include hexamethylene diisocyanate,diphenylmethane diisocyanate, tolylene diisocyanate, isophoronediisocyanate, tetramethylene diisocyanate, xylylene diisocyanate, lysinediisocyanate, an adduct of tolylene diisocyanate and trimethylolpropane,and an adduct of hexamethylene diisocyanate and trimethylolethane, etc.

[0082] Examples of the chain extension agent includependant-carboxyl-group-containing diols; glycols such as ethyleneglycol, diethylene glycol, propylene glycol, 1,4-butanediol,hexamethylene glycol, and neopentyl glycol; and diamines such asethylenediamine, propylenediamine, hexamethylenediamine,phenylenediamine, tolylenediamine, diphenyldiamine,diaminodiphenylmethane, diaminodiphenylmethane, anddiaminocyclohexylmethane, etc.

[0083] A specific example of the polyesterpolyurethane-based resinincludes “Hydran” (type name: AP-40F, etc.) manufactured by DainipponInk and Chemicals, Inc., etc.

[0084] In forming the coating layer, at least one ofN-methylpyrrolidone, ethylcellosolve acetate, and dimethylformamide aswater-soluble organic solvents is preferably added to the coatingmaterial to improve the coating-layer formability and increase theadhesion of the coating layer to the base layer. Particularly,N-methylpyrrolidone is preferred since it has a significant effect ofimproving the coating-layer formability and increasing the adhesion ofthe coating layer to the base layer. Preferably, the content of thewater-soluble organic solvent is 1 to 15 parts by weight, and morepreferably 3 to 10 parts by weight relative to 100 parts by weight ofthe polyesterpolyurethane-based resin from the point of view offlammability of the coating material and odor control.

[0085] Preferably, a crosslinking structure is introduced into thewater-dispersible polyesterpolyurethane-based resin so as to increasethe adhesion between the coating layer and the base layer. Examples ofthe method for obtaining such a coating material include methodsdisclosed in Japanese Unexamined Patent Application Publication Nos.63-15816, 63-256651, and 5-152159. At least one crosslinking agentselected from isocyanate compounds, epoxy compounds, and amine compoundsis added as the crosslinking component. These crosslinking agents formcrosslinks with the polyesterpolyurethane-based resin described aboveand thus increase the adhesion between the base layer and themetallization layer.

[0086] Examples of the isocyanate compounds used as the crosslinkingagents include toluene diisocyanate, xylene diisocyanate, naphthalenediisocyanate, hexamethylene diisocyanate, and isophorone diisocyanate,etc., described above. However, it is not limited to these isocyanatecompounds.

[0087] Examples of the epoxy compounds used as the crosslinking agentsinclude diglycidyl ether of bisphenol A and oligomers thereof,diglycidyl ether of hydrogenated bisphenol A and oligomers thereof,diglycidyl ether ortho-phthalate, diglycidyl ether isophthalate,diglycidyl ether terephthalate, and diglycidyl ether adipate, etc.However, it is not limited to these epoxy compounds.

[0088] Examples of the amine compounds used as the crosslinking agentsinclude amine compounds such as melamine, urine, and benzoguanamine,etc.; amino resins obtained by addition condensation of theabove-described amino compounds with formaldehyde or C₁-C₆ alcohol;hexamethylenediamine; and triethanolamine, etc. However, it is notlimited to these amine compounds.

[0089] An amine compound is preferably contained in the coating layerfrom the point of view of food hygiene and adhesion to the basematerial. A specific example of the amine compound used as thecrosslinking agent is “Beckamine” (type name: APM, etc.) manufactured byDainippon Ink and Chemicals, Inc., etc.

[0090] The amount of the crosslinking agent selected from isocyanatecompounds, epoxy compounds, and amine compounds is preferably 1 to 15parts by weight, and more preferably 3 to 10 parts by weight relative to100 parts by weight of the mixed coating material containing thewater-soluble polyesterpolyurethane-based resin and the water-solubleorganic solvent from the point of view of improving the chemicalresistance and preventing degradation in the water-proof property. Whenthe amount of the crosslinking agent is less than 1 part by weight, theeffect of improving the adhesion may not be obtained. At an amountexceeding 15 parts by weight, the adhesion between the coating layer andthe base layer may be degraded presumably due to the unreacted remainingcrosslinking agent.

[0091] Moreover, a small amount of a crosslinking accelerator may beadded to the coating layer so that the coating layer compositiondescribed above can completely form crosslinks and cure within the timetaken to manufacture the film for metallization.

[0092] The crosslinking accelerator contained in the coating layer ispreferably a water-soluble acidic compound since it has a significantcrosslinking promoting effect. Examples of the crosslinking acceleratorinclude terephthalic acid, isophthalic acid, 2,6-naphthalenedicarboxylic acid, adipic acid, trimethyladipic acid, sebacic acid,malonic acid, dimethylmalonic acid, succinic acid, glutaric acid,sulfonic acid, pimelic acid, 2,2-dimethylglutaric acid, azelaic acid,fumaric acid, maleic acid, itaconic acid, 1,3-cyclopentane dicarboxylicacid, 1,2-cyclohexane dicarboxylic acid, 1,4-cyclohexane dicarboxylicacid, 1,4-naphthalic acid, diphenic acid, 4,4′-hydroxy benzoic acid, and2,5-naphthalene dicarboxylic acid, etc.

[0093] A specific example of the crosslinking accelerator is “Catalyst”(type name: PTS, etc.) manufactured by Dainippon Ink and Chemicals,Inc., etc.

[0094] Moreover, inert particles may be added to the coating layer.Examples of the inert particles include inorganic fillers such assilica, alumina, calcium carbonate, barium sulfate, magnesium oxide,zinc oxide, and titanium oxide, and organic polymer particles such ascrosslinked-polystyrene particles, crosslinked-acryl particles, andcrosslinked-silicon particles, etc. In addition to the inert particles,a wax-based lubricant and a mixture of these, etc. may be added.

[0095] The coating layer is preferably formed on at least one side ofthe base layer to a thickness of 0.05 to 2 μm. When the thickness of thecoating layer is less than 0.05 μm, the adhesion to the base layer isdecreased, and coating defect may be formed, resulting in degradation ofthe gas barrier property after metallization. When the thickness of thecoating layer exceeds 2 μm, the time required for curing of the coatinglayer becomes longer, and the crosslinking reaction described above maybe incomplete, thereby degrading the gas barrier property. Moreover,when the coating layer is formed on the base layer during thefilm-forming process, the reclaimability of the film scraps to the baselayer is degraded, and numerous inner voids are formed by the resin ofthe coating layer which acts as the nuclei, thereby degrading themechanical properties.

[0096] The adhesive strength between the coating layer and the baselayer is preferably 0.6 N/cm or more. When the adhesive strength betweenthe coating layer and the base layer is less than 0.6 N/cm, the coatinglayer may peel off during converting, thereby imposing a significantlylarge limitation on the usage. The adhesive strength between the coatinglayer and the base layer is preferably 0.8 N/cm or more, and morepreferably 1.0 N/cm or more.

[0097] When a coating layer is formed on at least one side of thebiaxially stretched polypropylene film of the first, second, third, andfourth embodiments of the present invention so that the film can be usedas the film for metallization, the centerline average roughness (Ra) ofthe biaxially stretched polypropylene film of the first, second, third,and fourth embodiments of the present invention is preferably 0.01 to0.5 μm from the point of view of handling convenience, slipperiness, andblocking prevention. More preferably, the centerline average roughnessis 0.02 to 0.2 am. When the centerline average roughness (Ra) is lessthan 0.02 μm, the slipperiness may be degraded, resulting in thedegradation of handling convenience of the film. At a centerline averageroughness (Ra) exceeding 0.2 μm, pinholes may occur in an aluminum layerwhen a metallized film is made by sequentially depositing the coatinglayer and a metallization layer, thereby degrading the gas barrierproperty.

[0098] When a coating layer is formed on at least one side of thebiaxially stretched polypropylene film of the first, second, third, andfourth embodiments of the present invention so that the film can be usedas the film for metallization, the surface gloss of the biaxiallystretched polypropylene film of the first, second, third, and fourthembodiments of the present invention is preferably 135% or more, andmore preferably 138% or more to ensure superior metallic gloss aftermetallization.

[0099] In the present invention, the coating layer is preferably formedby a process of applying a coating solution using a reverse roll coater,a gravure coater, a rod coater, an air doctor coater, or other coatingmachines outside the polypropylene film manufacturing process. Morepreferably, the coating is performed in the film manufacturing process.More preferably, examples thereof include a method to apply coatingsolutions during the film manufacturing process, in which a coatingsolution is applied on an unstretched polypropylene film and then thefilm is sequentially biaxially stretched, and in which a coatingsolution is applied on a uniaxially stretched polypropylene film andthen the film is stretched in the direction perpendicular to theuniaxial stretching. This method in which a coating solution is appliedon a uniaxially stretched polypropylene film and then stretching thefilm in the direction perpendicular to the uniaxial stretching is mostpreferred since the thickness of the coating layer can be uniform andthe production efficiency can be improved.

[0100] When the biaxially stretched polypropylene film of the first,second, third, and fourth embodiments of the present invention is usedas the film for metallization, the polypropylene used in the base layerpreferably contains no organic lubricants such as fatty acid amide, etc.in point of view of adhesion of the coating layer and the metallizationlayer. However, a small amount of organic crosslinked particles orinorganic particles may be added to provide slipperiness and improve theprocessability and windability. Examples of the organic crosslinkedparticles added to the polypropylene of the base layer at a small amountinclude crosslinked-silicone particles,crosslinked-polymethylmethacrylate particles, andcrosslinked-polystyrene particles. Examples of the organic particlesinclude zeolite, calcium carbonate, silicon oxide, and aluminumsilicate. The average size of these particles is preferably 0.5 to 5 μmsince the slipperiness can be increased without significantly degradingthe transparency of the film of the present invention.

[0101] An antistatic for avoiding the troubles resulting from the staticelectrification of the film is preferably added to the biaxiallystretched polypropylene film of the first, second, third, and fourthembodiments of the present invention except for when the film is used asthe film for metallization having the above-described construction. Theantistatic agent contained in the biaxially stretched polypropylene filmof the first, second, third, and fourth embodiments of the presentinvention is not restricted. However, examples of the antistatic agentinclude ethylene oxide adducts of betaine derivatives, quaternary aminecompounds, alkyldiethanolamine fatty acid esters, glycerin fatty acidester, gylceride stearates, etc. and mixtures of these.

[0102] A lubricant is preferably added to the biaxially stretchedpolypropylene film of the first, second, third, and fourth embodimentsof the present invention, more preferably, in addition to the antistaticagent described above, except for when the film is used as the film formetallization having the above-described construction. The lubricant isadded to improve the mould-releasing property and the flowability duringthermo-forming of thermoplastic resins according to the wordings ofJapanese Industrial Standards, and to adjust the frictional forcebetween a converting machine and the film surface and between the filmsthemselves.

[0103] The lubricant added to the biaxially stretched polypropylene filmof the first, second, third, and fourth embodiments of the presentinvention is not restricted. However, examples of the lubricant includeamide compounds such as stearamide, erucic amide, erucamide, oleamide,etc. and mixtures of these.

[0104] The content of the antistatic agent added to the biaxiallystretched polypropylene film of the first, second, third, and fourthembodiments of the present invention is preferably 0.3 part by weight ormore, and more preferably in the range of 0.4 to 1.5 parts by weightrelative to 100 parts by weight of the polypropylene resin used. Thetotal content of the antistatic agent and the lubricant is morepreferably 0.5 to 2.0 parts by weight from the point of view ofantistatic property and slipperiness.

[0105] Inorganic particles and/or crosslinked organic particles forincreasing the slipperiness are preferably contained in the biaxiallystretched polypropylene film of the first, second, third, and fourthembodiments of the present invention.

[0106] In the present invention, the term “inorganic particles” refersto inorganic particles of metal compounds, and the inorganic particlesare not restricted. However, examples of inorganic particles includeparticles of zeolite, calcium carbonate, magnesium carbonate, alumina,silica, aluminum silicate, kaolin, kaolinite, talc, clay, diatomite,montmorillonite, and titanium oxide, etc. and mixtures of these.

[0107] In the present invention, the term “crosslinked organicparticles” refers to particles in which polymer compounds arecrosslinked by a crosslinking agent. The crosslinked organic particlescontained in the biaxially stretched polypropylene film of the first,second, third, and fourth embodiments of the present invention are notrestricted. However, examples of crosslinked organic particles includecrosslinked particles of polymethoxysilane-based compounds, crosslinkedparticles of polystyrene-based compounds, crosslinked particles ofacrylic-based compounds, crosslinked particles of polyurethane-basedcompounds, crosslinked particles of polyester-based compounds,crosslinked particles of fluoric-based compounds, and mixtures of these.

[0108] The average particle size of the inorganic particles andcrosslinked organic particles is preferably in the range of 0.5 to 6 μm.If an average particle size of is less than 0.5 μm, the slipperiness maybe degraded. If an average particle size exceeds 6 μm, drop-off ofparticles may occur, and the film surface may be readily damaged whenthe films come into contact with each other.

[0109] The amount of the inorganic particles and/or the crosslinkedorganic particles added is preferably in the range of 0.02 to 0.5percent by weight, and more preferably 0.05 to 0.2 percent by weightfrom the point of view of blocking prevention, slipperiness, andtransparency.

[0110] In addition to the above-described additives, a nucleating agent,a heat stabilizer, and an antioxidant may be added to the biaxiallystretched polypropylene film of the first, second, third, and fourthembodiments of the present invention, if necessary.

[0111] Examples of the nucleating agent include sorbitol-based,organic-metal-phosphate-ester-based, organic-metal-carboxylate-based,and rosin-based nucleating agents. The amount of the nucleating agent is0.5 percent by weight or less. As the heat stabilizer,2,6-di-tertiary-butyl-4-methylphenol (BHT) or the like may be added inan amount of 0.5 percent by weight or less. As the antioxidant,tetrakis-(methylene-(3,5-di-tertiary-butyl-4-hydroxy-hydrocinnamate))butane(Irganox 1010) or the like may be added in amount of 0.5 percent byweight or less.

[0112] A publicly known polyolefin resin is preferably laminated on atleast one side of the biaxially stretched polypropylene film of thefirst, second, third, and fourth embodiments of the present inventionfor the purposes other than those described above, such as prevention ofbleed-out/flying-off of additives, adhesion of the metallization layer,high printability, enhancement of heat sealability, enhancement of printlamination property, enhancement of glossy appearance, haze reduction(enhancement of transparency), enhancement of releasing property, andenhancement of slipperiness, etc.

[0113] The thickness of the laminated polyolefin resin is preferably0.25 μm or more and half the total thickness of the film or less. If thethickness is less than 0.25 μm, it is difficult to form a uniform layerdue to lamination defects. When the thickness exceeds half the totalthickness of the film, the effect of the surface layer on the mechanicalproperty becomes large, resulting in a decrease in Young's modulus andtension resistance of the film. This resin laminated on the surface neednot satisfy the ranges of the present invention. Examples of thelamination method include co-extrusion, in-line/off-line extrusionlamination and in-line/off-line coating, etc. The method is not limitedto these, and the most suitable method should be selected as needed.

[0114] At least one film surface of the biaxially stretchedpolypropylene film of the first, second, third, and fourth embodimentsof the present invention is preferably subjected to corona dischargetreatment so as to allow the film surface to have a surface wettingtension of at least 35 mN/m because the printability, adhesion,antistatic property, and lubricant bleed-out property can be improved.The atmospheric gas during corona discharge treatment is preferably air,oxygen, nitrogen, carbon dioxide gas, or a nitrogen/carbon dioxidemixture gas. From the point of view of economical efficiency, coronadischarge treatment in air is particularly preferred.

[0115] The Young's modulus in the longitudinal direction (Y(MD)) at 25°C. of the biaxially stretched polypropylene film of the first, second,third, and fourth embodiments of the present invention is preferably 2.5GPa or more. When the Y(MD) at 25° C. is less than 2.5 GPa, thestiffness in the transverse direction becomes high when compared withthat in the longitudinal direction, resulting in an imbalance ofstiffness and insufficient firmness of the film. As a result, pitchdisplacement may occur during printing, elongation of the film may occurduring laminating, and cracks may occur if the film is subjected tocoating/metallization processes. In other words, the film may exhibitinsufficient tension resistance. The Young's modulus in the longitudinaldirection (Y(MD)) at 25° C. can be controlled by adjusting thetemperature of cooling drum for cooling and solidifying the moltenmaterial to prepare an unstretched sheet, the conditions for thelongitudinal stretching (temperature, stretching ratio, etc.), thecrystallinity of the polypropylene (depending on mmmm, II, etc.), theamount of the additive for providing plasticity during stretching, andthe like. The optimum film forming conditions and raw materials shouldbe selected as needed, as long as the advantages of the presentinvention are not impaired. The Young's modulus in the longitudinaldirection (Y(MD)) at 25° C. is more preferably 2.7 GPa or more, morepreferably 3.0 GPa or more, and most preferably 3.2 GPa or more.

[0116] The Young's modulus in the longitudinal direction (Y(MD)) at 80°C. of the biaxially stretched polypropylene film of the first, second,third, and fourth embodiments of the present invention is preferably 0.4GPa or more. When the Y(MD) at 80° C. is less than 0.4 GPa, the tensionresistance during film converting may be insufficient. The Young'smodulus in the longitudinal direction (Y(MD)) at 80° C. can becontrolled by adjusting the temperature of cooling drum for cooling andsolidifying the molten material to prepare an unstretched sheet, theconditions for the longitudinal stretching (temperature, stretchingratio, etc.), the crystallinity of the polypropylene (depending on mmmm,II, etc.), the amount of the additive for providing plasticity duringstretching, and the like. The optimum film forming conditions and rawmaterials should be selected as needed, as long as the advantages of thepresent invention are not impaired. The Young's modulus in thelongitudinal direction (Y(MD)) at 80° C. is more preferably 0.5 GPa ormore, and furthermore preferably 0.6 GPa or more.

[0117] In the biaxially stretched polypropylene film of the first,second, third, and fourth embodiments of the present invention, the mvalue at 25° C. is preferably in the range of 0.4 to 0.7 wherein the mvalue in terms of a Young's modulus in the longitudinal direction(Y(MD)) and a Young's modulus in the transverse direction (Y(TD)) isexpressed as below:

m=Y(MD)/(Y(MD)+Y(TD))

[0118] Here, the m value is the ratio of the Young's modulus in thelongitudinal direction to the total of the Young's moduli in thelongitudinal and transverse directions. Accordingly, a film having an mvalue of less than 0.5 has a higher stiffness in the transversedirection than in the longitudinal direction. A film having an m valueof 0.5 has a substantially balanced stiffness between the stiffness inthe longitudinal direction and the stiffness in the transversedirection. A film having an m value of more than 0.5 has a higherstiffness in the longitudinal direction than in the transversedirection. When a film has an m value of 0.4 to 0.7, the film hasbalanced and high stiffness. When the m value at 25° C. is less than0.4, the stiffness in the longitudinal direction is significantly lowerthan that in the transverse direction, resulting in an imbalance of thestiffness. This may result in insufficient tension resistance duringfilm converting and insufficient film stiffness and is therefore notpreferred. An m value exceeding 0.7 is also not preferred since thestiffness in the transverse direction may be significantly lower thanthat in the longitudinal direction and the firmness of the resultingfilm may be insufficient.

[0119] The m value at 25° C. can be controlled by adjusting thefilm-forming conditions, e.g., the temperature of cooling drum forcooling and solidifying the molten material to prepare an unstretchedsheet, the temperatures during longitudinal/transverse stretching,stretching ratio, relaxation of the film after longitudinal/transversestretching, the crystallinity of the polypropylene (depending on mmmm,II, etc.), the amount of the additive for providing plasticity duringstretching, and the like. The optimum film-forming conditions and rawmaterials should be selected as needed, as long as the advantages of thepresent invention are not impaired. The m value at 25° C. is morepreferably 0.42 to 0.68, more preferably 0.44 to 0.65, and mostpreferably 0.46 to 0.62. Preferably, the m value at 80° C. is also inthe range of 0.4 to 0.7.

[0120] The F2 value in the longitudinal direction at 25° C. of thebiaxially stretched polypropylene film of the first, second, third, andfourth embodiments of the present invention is preferably 40 MPa ormore. Here, the F2 value in the longitudinal direction is a stressapplied on a sample 15 cm in the longitudinal direction and 1 cm in thetransverse direction at an elongation of 2% when the sample is stretchedat an original length of 50 mm and a testing speed of 300 mm/min. Whenthe F2 value in the longitudinal direction at 25° C. is less than 40MPa, pitch displacement may occur during printing, elongation of thefilm may occur during laminating, and cracks may occur if the film issubjected to coating/metallization processes. In other words, the filmmay exhibit insufficient tension resistance. The F2 value in thelongitudinal direction at 25° C. is more preferably 45 MPa or more.

[0121] The F5 value in the longitudinal direction at 25° C. of thebiaxially stretched polypropylene film of the first, second, third, andfourth embodiments of the present invention is preferably 50 MPa ormore. Here, the F5 value in the longitudinal direction is a stressapplied on a sample 15 cm in the longitudinal direction and 1 cm in thetransverse direction at an elongation of 5% when the sample is stretchedat an original length of 50 mm and a testing speed of 300 mm/min. Whenthe F5 value in the longitudinal direction at 25° C. is less than 50MPa, pitch displacement may occur during printing, elongation of thefilm may occur during laminating, and cracks may occur if the film issubjected to coating/metallization processes. In other words, the filmmay exhibit insufficient tension resistance. The F5 value in thelongitudinal direction at 25° C. is more preferably 55 MPa or more.

[0122] The heat shrinkage in the longitudinal direction at 120° C. ofthe biaxially stretched polypropylene film of the first, second, third,and fourth embodiments of the present invention is preferably 5% orless. When the heat shrinkage in the longitudinal direction at 120° C.exceeds 5%, an extensive degree of shrinking occurs when the film isheated during processes such as printing, laminating, coating,metallization, and the like, resulting in process failures such asdefects in the film, pitch displacement, and wrinkles. The heatshrinkage in the longitudinal direction at 120° C. can be controlled byadjusting the temperature of cooling drum for cooling and solidifyingthe molten material to prepare an unstretched sheet, the conditions forthe longitudinal stretching (stretching temperature, stretching ratio,relaxation of the film after longitudinal stretching, etc.), thecrystallinity of the polypropylene (depending on mmmm, II, etc.), theamount of the additive for providing plasticity during stretching, andthe like. The optimum longitudinal-stretching conditions and rawmaterials should be selected as needed, as long as the advantages of thepresent invention are not impaired. More preferably, the heat shrinkagein the longitudinal direction at 120° C. is 4% or less.

[0123] In the biaxially stretched polypropylene film of the first,second, third, and fourth embodiments of the present invention, the sumof the heat shrinkage in the longitudinal direction and the heatshrinkage in the transverse direction at 120° C. is preferably 8% orless, and more preferably 6% or less. When the sum of the heat shrinkagerates in the longitudinal and transverse directions exceeds 8%, anextensive degree of shrinking occurs when the film is heated duringprocesses such as printing, laminating, coating, metallization, and thelike, resulting in process failures such as defects in the film, pitchdisplacement, and wrinkles. The sum of the heat shrinkages in thelongitudinal and transverse directions can be controlled by adjustingthe film-forming conditions, e.g., the temperature of cooling drum forcooling and solidifying the molten material to prepare an unstretchedsheet, the temperatures during longitudinal/transverse stretching,stretching ratio, relaxation of the film after longitudinal/transversestretching; the crystallinity of the polypropylene (depending on mmmm,II, etc.); the amount of the additive for providing plasticity duringstretching; and the like. The optimum film-forming conditions and rawmaterials should be selected as needed, as long as the advantages of thepresent invention are not impaired. More preferably, the sum of the heatshrinkages in the longitudinal and transverse directions at 120° C. is6% or less.

[0124] The water vapor permeability of the biaxially stretchedpolypropylene film of the first, second, third, and fourth embodimentsof the present invention is preferably 1.5 g/m²/d/0.1 mm or less. Whenthe water vapor permeability exceeds 1.5 g/m²/d/0.1 mm, the biaxiallystretched polypropylene film of the present invention may exhibit poormoisture-proof property when it is used as a packaging material thatshields the contents from the external air. The water vapor permeabilitycan be controlled by adjusting the film-forming conditions, e.g., thetemperature of cooling drum for cooling and solidifying the moltenmaterial to prepare an unstretched sheet, the temperatures duringlongitudinal/transverse stretching, stretching ratio; the crystallinityof the polypropylene (depending on mmmm, II, etc.); the amount of theadditive for providing plasticity during stretching; and the like. Theoptimum film-forming conditions and raw materials should be selected asneeded as long as the advantages of the present invention are notimpaired. More preferably, the water vapor permeability is 1.2g/m²/d/0.1 mm or less.

[0125] Preferably, the biaxially stretched polypropylene film of thefirst, second, third, and fourth embodiments of the present inventionincludes longitudinal fibrils having a width of 40 nm or more andextending across two sides parallel to the transverse direction in a1-μm square film surface one side of which is parallel to thelongitudinal direction.

[0126] The term “longitudinal fibrils” refers to the fibrils oriented inthe longitudinal direction when the film surface is observed with anatomic force microscope (AFM). The longitudinal fibrils include fibrilshaving undulating shapes and branching shapes to some extent. Moreover,the longitudinal fibrils may be tilted to a certain extent from an axisin the longitudinal direction depending on the position of theobservation. The longitudinal fibrils include those preferentiallyoriented in the longitudinal direction rather than the transversedirection within ±45° with respect to the axis in the longitudinaldirection.

[0127] In the present invention, observation with an atomic forcemicroscope (AFM) is performed 5 times at different positions in a 1-μmsquare field view one side of which is parallel to the longitudinaldirection. A film is defined to have longitudinal fibrils if one or morelongitudinal fibrils having a width of 40 nm or more and extendingacross two sides parallel to the transverse direction are observed inall of the acquired images. Preferably, longitudinal fibrils areobserved in both surfaces of the film. Alternatively, longitudinalfibrils in only one surface may be observed.

[0128] Because the longitudinal fibrils described above are introducedin the first, second, third, and fourth embodiments of the presentinvention, the stiffness of the film in the longitudinal direction canbe significantly increased. This is because the longitudinal fibrilsrarely deform when stress is applied in the longitudinal direction ofthe film.

[0129] The longitudinal fibrils in the biaxially stretched polypropylenefilm of the first, second, third, and fourth embodiments of the presentinvention extend across two sides parallel to the transverse directionin a 1-μm square film surface, one side of which is parallel to thelongitudinal direction. The longitudinal fibrils preferably extendacross two sides parallel to the transverse direction in a 5-μm squarefilm surface one side of which is parallel to the longitudinaldirection, and more preferably across two sides parallel to thetransverse direction in a 10-μm square film surface one side of which isparallel to the longitudinal direction.

[0130] In the biaxially stretched polypropylene films of the first,second, third, and fourth embodiments of the present invention, theYoung's modulus in the longitudinal direction can be sufficiently highand thereby a sufficient tension resistance can be achieved if one ormore longitudinal fibrils are present in the 1-μm square film surfaceone side of which is parallel to the longitudinal direction. The numberof longitudinal fibrils is more preferably 2 or more, and furthermorepreferably 3 to 10. Here, a branching longitudinal fibril is counted asone fibril. When no longitudinal fibrils extending across two sidesparallel to the transverse direction in the 1-μm square film surface oneside of which is parallel to the longitudinal direction are present, thefibril structure may readily deform in the longitudinal direction,possibly resulting in a decrease in stiffness of the film in thelongitudinal direction and in insufficient tension resistance of thefilm.

[0131] The Young's modulus of the film in the longitudinal directiontends to increase as the number of the longitudinal fibrils describedabove increases. However, when the number is excessively large, thesurface haze may become high. More preferably, the number of thelongitudinal fibrils in the biaxially stretched polypropylene films ofthe first, second, third, and fourth embodiments of the presentinvention in a 5-μm square film surface one side of which is parallel tothe longitudinal direction is 1 or more, more preferably, 2 or more, andfurthermore preferably in the range of 3 to 10.

[0132] Furthermore preferably, the number of the longitudinal fibrils inthe biaxially stretched polypropylene films of the first, second, third,and fourth embodiments of the present invention in a 10-μm square filmsurface one side of which is parallel to the longitudinal direction is 1or more, more preferably, 2 or more, and most preferably in the range of3 to 10.

[0133] In the biaxially stretched polypropylene films of the first,second, third, and fourth embodiments of the present invention,preferably, one or more longitudinal fibrils are present in a 1-μmsquare film surface one side of which is parallel to the longitudinaldirection. A sufficient number of longitudinal fibrils are present ifthe above-described ranges are satisfied. Accordingly, a film having afibril structure, which is difficult to deform, sufficient tensionresistance, glossy surface, and superior gas barrier property can beobtained.

[0134] The width of the longitudinal fibrils in the biaxially stretchedpolypropylene films of the first, second, third, and fourth embodimentsof the present invention is preferably 40 nm or more from the point ofview of providing sufficient tension resistance by increasing theYoung's modulus in the longitudinal direction of the film. Here, theterm “width of the longitudinal fibril” refers to an average value ofwidths of the longitudinal fibrils measured along three straight linesextending in the transverse direction in an image observed with theatomic force microscope (AFM). The three straight lines are drawn atregular interval between two sides of the image, which is parallel tothe transverse direction, so as to divide the image into four equalsegments. The width of the branching longitudinal fibrils is measured asfollows. The width of the portion of the fibril containing no branchingis measured as above. As for the branching portions, the sum of thewidths of all the branching portions measured along the straight linesparallel to the transverse direction is calculated. When the width ofthe longitudinal fibrils is less than 40 nm, the longitudinal fibrilsmay readily deform when a stress is applied in the longitudinaldirection of the film. As a result, the Young's modulus in thelongitudinal direction may become insufficient, and the tensionresistance may become poor. The Young's modulus in the longitudinaldirection of the film tends to increase as the width of the longitudinalfibrils increases. However, when the widths of the longitudinal fibrilsare excessively large, the surface haze may become high. The width ofthe longitudinal fibrils in the biaxially stretched polypropylene filmof the present invention is preferably in the range of 50 to 500 nm,more preferably 55 to 200 nm, and most preferably 60 to 200 nm. A filmhaving sufficient tension resistance and excellent surface haze and gasbarrier property can be obtained when the width of the longitudinalfibrils in the biaxially stretched polypropylene films of the first,second, third, and fourth embodiments of the present invention is 40 nmor more.

[0135] The fibril structure of the biaxially stretched polypropylenefilm of the present invention preferably includes a fine network offibrils, having a width of about 20 nm, growing from the above-describedlongitudinal fibrils. With such a structure, the film can be highlyfirm.

[0136] Publicly known methods may be employed in manufacturing thebiaxially stretched polypropylene films of the first, second, third, andfourth embodiments of the present invention. For example, apolypropylene which comprises a polypropylene satisfying formula (1)described above,

log(MS)>−0.61 log(MFR)+0.82   (1)

[0137] or a polypropylene which consists of a polypropylene satisfyingformula (2) described above,

log(MS)>−0.61 log(MFR)+0.52   (2)

[0138] or a polypropylene which comprises a polypropylene having aTrouton ratio of 30 or more, or a polypropylene which consists of apolypropylene having a Trouton ratio of 16 or more is blended with atleast one of petroleum resins substantially containing no polar-groupand/or terpene resins substantially containing no polar-group, and themixture is fed into an extruder. The mixture is melted at a temperatureof 200 to 290° C., filtered, and extruded from a slit die. The extrudedmixture is then wound around a cooling drum to be cooled and solidifiedinto a sheet so as to make an unstretched film. The temperature of thecooling drum is preferably 20 to 100° C. so that the film can beadequately crystallized. In this manner, a large number of longitudinalfibrils having a large length can be obtained after biaxiallystretching.

[0139] Next, the resulting unstretched film is biaxially stretched by apublicly known longitudinal-transverse sequential biaxial stretchingmethod. The important factor for making a biaxially stretchedpolypropylene film highly tensilized in the longitudinal direction isthe stretching ratio in the longitudinal direction. The reallongitudinal stretching ratio in a conventional longitudinal-transversesequential biaxial stretching method for making a polypropylene film isin the range of 4.5 to 5.5, and if a longitudinal stretching ratioexceeds 6, film-forming may become unstable, and the film may breakduring transverse stretching. On the contrary, in the present invention,the real longitudinal stretching ratio is preferably 6 or more. If areal longitudinal stretching ratio is less than 6, sufficientlongitudinal fibrils may not be obtained, the stiffness in thelongitudinal direction of the film may be insufficient, and the firmnessof the resulting film may be insufficient in making the thinner film.The more preferable real stretching ratio in the longitudinal directionis 7 or more, and the furthermore preferable real longitudinalstretching ratio is 8 or more. It is sometimes preferable to perform thelongitudinal stretching in two or more steps from the point of view oftensilization in the longitudinal direction and introduction of thelongitudinal fibrils. The longitudinal stretching temperature is anoptimum temperature selected from the point of view of stability infilm-forming, tensilization in the longitudinal direction, andintroduction of the longitudinal fibrils. The longitudinal stretchingtemperature is preferably 120 to 150° C. Moreover, during the coolingprocess that follows longitudinal stretching, the film is preferablyrelaxed in the longitudinal direction to an extent that does not furtherinduce thickness irregularity of the film from the point of view ofdimensional stability in the longitudinal direction.

[0140] The real stretching ratio in the transverse direction ispreferably 10 or less. If a real transversal stretching ratio exceeding10, the stiffness of the resulting film in the longitudinal directionmay be low, the number of longitudinal fibrils may decrease, and thefilm-forming may become unstable. The transversal stretching temperatureis an optimum temperature selected from the point of view of stabilityin film-forming, thickness irregularities, tensilization in thelongitudinal direction, and introduction of the longitudinal fibrils.The transversal stretching temperature is preferably 150 to 180° C.

[0141] After stretching in the transverse direction, the film isheat-set at 150 to 180° C. while relaxing the film in the transversedirection by 1% or more, cooled, and wound to obtain the biaxiallystretched polypropylene film of the present invention.

[0142] An example method for manufacturing a film for metallizationusing a biaxially stretched polypropylene films of the first, second,third, and fourth embodiments of the present invention will now bedescribed. However, the present invention is not limited by themanufacturing method described below.

[0143] For example, a polypropylene which comprises a polypropylenesatisfying formula (1) described above,

log(MS)>−0.61 log(MFR)+0.82   (1)

[0144] or a polypropylene which consists of a polypropylene satisfyingformula (2) described above,

log(MS)>−0.61 log(MFR)+0.52   (2)

[0145] or a polypropylene which comprises a polypropylene having aTrouton ratio of 30 or more, or a polypropylene which consists of apolypropylene having a Trouton ratio of 16 or more is blended with atleast one of petroleum resins substantially containing no polar-groupand/or terpene resins substantially containing no polar-group. The mixedresin and/or the third layer resin are prepared. These resins are fedinto separate extruders, melted at 200 to 290° C., and are filtered. Theresins are put together inside a short pipe or a die, extruded from aslit die to form a laminate each layer of which has a target thickness,and wound around a cooling drum so as to be cooled and solidified into asheet so as to make an unstretched laminate film. The temperature of thecooling drum is preferably 20 to 100° C. so that the film can beadequately crystallized. In this manner, a large number of longitudinalfibrils having a large length can be obtained after biaxiallystretching.

[0146] The unstretched laminate film is heated to a temperature of 120to 150° C. and stretched in the longitudinal direction to 6 times theinitial length or more. The film is then fed into a tenter-type drawingmachine so as to stretch the film in the transverse direction to 10times the initial length or less at 150 to 180° C., relaxed by heatingat 150 to 180° C., and cooled. If necessary, a surface of the base layeron which a metallization layer is to be deposited and/or the thirdsurface opposite of the base layer is subjected to corona dischargetreatment in air, nitrogen, or mixture gas of carbon dioxide andnitrogen. When a heat-seal layer is to be laminated as a third layer,corona discharge treatment is preferably avoided to achieve highadhesive strength. Next, the film is wound to obtain a biaxiallystretched polypropylene film for metallization.

[0147] To make a film having a superior gas barrier property, theabove-described unstretched laminate film is heated to a temperature of120 to 150° C., stretched in the longitudinal direction to 6 times theinitial length or more, and cooled. Subsequently, the above-describedcoating material is applied on the uniaxially stretched film base layer.The base layer surface may be subjected to corona discharge treatment,if necessary. The film is then fed into a tenter-type drawing machine,stretched at a temperature of 150 to 180° C. in the transverse directionto 10 times the initial length or less, relaxed by heating at 150 to180° C., and cooled. The resulting coating layer on the base layerand/or the third layer surface opposite of the base layer may besubjected to corona discharge treatment in air, nitrogen, or mixture gasof carbon dioxide and nitrogen if necessary. At this stage, when aheat-seal layer is to be laminated as a third layer, corona dischargetreatment is preferably avoided to achieve high adhesive strength. Next,the film is wound to obtain a biaxially stretched polypropylene film formetallization.

[0148] In the present invention, the biaxially stretched polypropylenefilm for metallization is preferably aged at 40 to 60° C. so as toaccelerate the reaction in the coating layer. When the reaction in thecoating layer is accelerated, the adhesive strength of the coating layerto the base layer and to the metallization layer can be increased, andgas barrier property of the film can be improved. Aging is preferablyperformed for 12 hours or more, and more preferably 24 hours or more toimprove the chemical resistance.

[0149] Next, the metallization is performed by vacuum metallization ofmetal. A metal from evaporation source is deposited on the coatinglayer, which coats the surface of the biaxially stretched polypropylenefilm of the present invention, to form a metallization layer.

[0150] Examples of the evaporation source include those of aresistance-heating boat type, a radiation- or radio-frequency-heatingcrucible type, and an electron beam heating type. The evaporation sourceis not restricted.

[0151] The metal used in the metallization is preferably a metal such asAl, Zn, Mg, Sn, Si, or the like. Alternatively, Ti, In, Cr, Ni, Cu, Pb,Fe, or the like may be used. These metals preferably have purities of99% or more, and more preferably 99.5% or more and are preferablyprocessed into grains, rods, tablets, wires, and crucibles.

[0152] Among the metals for metallization, an aluminum metallizationlayer is preferably formed on at least one side of the film from thepoint of view of durability of the metallization layer, productionefficiency, and cost. Other metal components such as nickel, copper,gold, silver, chromium, zinc, and the like may be metallizedsequentially or simultaneously with aluminum.

[0153] The metallization layer preferably has a thickness of 10 nm ormore, and more preferably 20 nm or more to achieve high gas barrierproperty. No limit is imposed as to the upper limit of the thickness ofthe metallization layer; however, the thickness is preferably less than50 nm from the point of view of economical and production efficiencies.

[0154] The gloss of the metallization layer is preferably 600% or more,and more preferably 700% or more.

[0155] Alternatively, a metallization layer composed of metal oxide maybe formed so that the film may be used as a transparent gas-barrier filmfor packaging having a superior gas barrier property. The metal oxidemetallization layer is preferably a layer of a metal oxide such asincompletely oxidized aluminum, or incompletely oxidized silicon.Incompletely oxidized aluminum is particularly preferable from the pointof view of durability of the metallization layer, production efficiency,and cost. Metallization can be performed by publicly known methods. Forexample, in depositing the metallization layer composed of incompletelyoxidized aluminum, the film is allowed to run in a high-vacuum devicehaving a degree of vacuum of 10⁻⁴ Torr or less, aluminum metal isheated, melted, and evaporated, and a small amount of oxygen gas issupplied at the site of evaporation so that the aluminum can becoherently deposited on the film surface to form a metallization layerwhile being oxidized. The thickness of the metal oxide metallizationlayer is preferably in the range of 10 to 50 nm, and more preferably 10to 30 nm. The oxidation of the metal oxide metallization layer composedof incompletely oxidized metal proceeds after metallization and changesthe light transmittance of the metal oxide metallized film. The lighttransmittance is preferably in the range of 70 to 90%. A lighttransmittance of less than 70% is not preferred since the content cannotbe seen through the package when the film is made into a packaging bag.A light transmittance exceeding 90% is not preferred because the gasbarrier property tends to be poor when the film is made into a packagingbag.

[0156] The adhesive strength between the metallization layer and thecoating layer of the metallized biaxially stretched polypropylene filmof the present invention and between the metal oxide metallization layerand the coating layer of the metallized biaxially stretchedpolypropylene of the present invention is preferably 0.6 N/cm or more,and more preferably 0.8 N/cm or more. When the adhesive strength is lessthan the above-described range, the metallization layer may be pickedoff when the metallized film is being wound into a roll and when themetallized film is being wound off for converting, resulting indegradation of the gas barrier properties.

[0157] The gas barrier properties of the films prepared by depositing ametallization layer of a metal and a oxide metal on the biaxiallystretched polypropylene films of the present invention are preferably asfollows. The water vapor permeability is preferably 4 g/m²/d or less,and more preferably 1 g/m²/d or less, and the oxygen permeability ispreferably 200 ml/m²/d/MPa or less, and more preferably 100 ml/m²/d/MPafor use in food packaging bags.

[0158] The biaxially stretched polypropylene films of the first, second,third, and fourth embodiments of the present invention have an increasedstiffness in the longitudinal direction compared with conventionalbiaxially stretched polypropylene films without degrading importantproperties such as dimensional stability and moisture-proof property. Asa result, the film exhibits superior handling convenience and excellenttension resistance against converting tension applied during filmconverting such as printing, laminating, coating, metallizing, andbag-making. Moreover, the troubles such as film cracks and print pitchdisplacement due to the quality of base films can be avoided.Furthermore, the stiffness in the longitudinal direction and the tensionresistance are higher than those of the conventional polypropylene filmshaving the same thickness; hence, the same degree of converting propertycan be maintained with a thickness smaller than that of conventionalbiaxially stretched polypropylene films. Accordingly, the biaxiallystretched polypropylene films of the present invention are suitable forpackaging and industrial use.

[0159] A fifth embodiment of the present invention is a biaxiallystretched polypropylene film characterized by including longitudinalfibrils having a width of 40 nm or more and extending across two sidesparallel to the transverse direction in a 1-μm square film surface oneside of which is parallel to the longitudinal direction.

[0160] The term “longitudinal fibrils” refers to the fibrils oriented inthe longitudinal direction when the film surface is observed with anatomic force microscope (AFM). The longitudinal fibrils include fibrilshaving undulating shapes and branching shapes to some extent. Moreover,the longitudinal fibrils may be tilted to a certain extent from an axisin the longitudinal direction depending on the position of theobservation. The longitudinal fibrils include those preferentiallyoriented in the longitudinal direction rather than the transversedirection within ±45° with respect to the axis in the longitudinaldirection.

[0161] In the present invention, observation with an atomic forcemicroscope (AFM) is performed 5 times at different positions in a 1-μmsquare field view one side of which is parallel to the longitudinaldirection. A film is defined to have longitudinal fibrils if one or morelongitudinal fibrils having a width of 40 nm or more and extendingacross two sides parallel to the transverse direction are observed inall of the acquired images. Preferably, longitudinal fibrils areobserved in both surfaces of the film. Alternatively, longitudinalfibrils in only one surface may be observed.

[0162] Because the longitudinal fibrils described above are introducedin the fifth embodiment of the present invention, the stiffness of thefilm in the longitudinal direction can be significantly increased. Thisis because the longitudinal fibrils rarely deform when stress is appliedin the longitudinal direction of the film.

[0163] The longitudinal fibrils in the biaxially stretched polypropylenefilm of the fifth embodiment of the present invention extend across twosides parallel to the transverse direction in a 1-μm square film surfaceone side of which is parallel to the longitudinal direction. Thelongitudinal fibrils preferably extend across two sides parallel to thetransverse direction in a 5-μm square film surface one side of which isparallel to the longitudinal direction, and more preferably across twosides parallel to the transverse direction in a 10-μm square filmsurface one side of which is parallel to the longitudinal direction.

[0164] In the biaxially stretched polypropylene film of the fifthembodiment of the present invention, the Young's modulus can besufficiently high and thereby a sufficient tension resistance can beachieved if one or more longitudinal fibrils are present in the 1-μmsquare film surface one side of which is parallel to the longitudinaldirection. The number of longitudinal fibrils is more preferably 2 ormore, and furthermore preferably 3 to 10. Here, a branching longitudinalfibril is counted as one fibril. When no longitudinal fibrils extendingacross two sides parallel to the transverse direction in the 1-μm squarefilm surface one side of which is parallel to the longitudinal directionare present, the fibril structure may readily deform in the longitudinaldirection, possibly resulting in a decrease in stiffness of the film inthe longitudinal direction and in insufficient tension resistance of thefilm.

[0165] The Young's modulus of the film in the longitudinal directionincreases as the number of the longitudinal fibrils increases. However,when the number is excessively large, the surface haze may become high.More preferably, the number of the longitudinal fibrils in the biaxiallystretched polypropylene film of the fifth embodiment of the presentinvention in a 5-μm square film surface one side of which is parallel tothe longitudinal direction is 1 or more, more preferably, 2 or more, andfurthermore preferably in the range of 3 to 10.

[0166] Furthermore preferably, the number of the longitudinal fibrils inthe biaxially stretched polypropylene film of the fifth embodiment ofthe present invention in a 10-μm square film surface one side of whichis parallel to the longitudinal direction is 1 or more, more preferably,2 or more, and furthermore preferably in the range of 3 to 10.

[0167] In the biaxially stretched polypropylene film of the fifthembodiment of the present invention, preferably, one or morelongitudinal fibrils are present in a 1-μm square film surface one sideof which is parallel to the longitudinal direction. A sufficient numberof longitudinal fibrils are present if the above-described ranges aresatisfied. Accordingly, a film having the fibril structure, which isdifficult to deform, sufficient tension resistance, glossy surface, andsuperior gas barrier property can be obtained.

[0168] The width of the longitudinal fibrils in the biaxially stretchedpolypropylene film of the fifth embodiment of the present invention is40 nm or more from the point of view of providing sufficient tensionresistance by increasing the Young's modulus in the longitudinaldirection of the film. Here, the term “width of the longitudinal fibril”refers to an average value of widths of the longitudinal fibrilsmeasured along three straight lines extending in the transversedirection in an image observed with the atomic force microscope (AFM).The three straight lines are drawn at regular interval between two sidesof the image, which is parallel to the transverse direction, so as todivide the image into four equal segments. The width of the branchinglongitudinal fibrils is measured as follows. The width of the portion ofthe fibril containing no branching is measured as above. As for thebranching portions, the sum of the widths of all the branching portionsmeasured along the straight lines parallel to the transverse directionis calculated. When the width of the longitudinal fibrils is less than30 nm, the longitudinal fibrils may readily deform when a stress isapplied in the longitudinal direction of the film. As a result, theYoung's modulus in the longitudinal direction may become insufficient,and the tension resistance may become poor. The Young's modulus in thelongitudinal direction of the film tends to increase as the width of thelongitudinal fibrils increases. However, when the widths of thelongitudinal fibrils are excessively large, the surface haze may becomehigh. The width of the longitudinal fibrils in the biaxially stretchedpolypropylene film of the fifth embodiment of the present invention ispreferably in the range of 50 to 500 nm, more preferably 55 to 250 nm,and most preferably 60 to 200 nm. A film having sufficient tensionresistance and excellent surface haze and gas barrier property can beobtained when the width of the longitudinal fibrils in the biaxiallystretched polypropylene film of the present invention is 40 nm or more.

[0169] The fibril structure of the biaxially stretched polypropylenefilm of the fifth embodiment of the present invention preferablyincludes a fine network of fibrils, having a width of about 20 nm,growing from the above-described longitudinal fibrils. With such astructure, the film can be highly firm.

[0170] Preferably, the biaxially stretched polypropylene film of thefifth embodiment of the present invention comprises a high-melt-strengthpolypropylene (HMS-PP) having higher melt strength (MS) than that ofconventional polypropylenes.

[0171] The melt strength (MS) and the melt flow rate (MFR) of the HMS-PPdescribed above measured at 230° C. preferably satisfy the formula:

log(MS)>−0.61 log(MFR)+0.82

[0172] The melt strength (MS) at 230° C. is measured by the followingprocess. Using a melt tension tester manufactured by Toyo Seiki KogyoCo., Ltd., the polypropylene is heated to 230° C., and the resultingmolten polypropylene is extruded at an extrusion rate of 15 mm/min toprepare a strand. The tension of the strand at a take-over rate of 6.5m/min is measured, and this tension is defined as the melt strength(MS). The unit therefor is cN.

[0173] The melt flow rate (MFR) at 230° C. is measured according toJapanese Industrial Standards (JIS) K 6758, whereby a melt flow rate(MFR) under a load of 2.16 kg is measured. The unit therefor is g/10min.

[0174] Preferably, the Trouton ratio of the HMS-PP described above is 30or more.

[0175] The Trouton ratio is measured by a converging flow methodaccording to a theory by Cogswell [Polymer Engineering Science, 12, 64(1972)]. The Trouton ratio is a ratio of the extensional viscosity toshear viscosity at 230° C. and a strain rate of 60 S⁻¹ calculated froman extensional viscosity-extensional strain rate curve and a shearviscosity-shear strain rate curve approximated by an exponentialfunction.

[0176] Generally, the higher the Trouton ratio of the HMS-PP describedabove, the more preferable. However, at an excessively high ratio, thefilm formability and surface haze may be degraded. The Trouton ratio ofthe HMS-PP described above is preferably 35 or more, and most preferablyin the range of 40 to 100.

[0177] Because the biaxially stretched polypropylene film of the fifthembodiment comprises the above-described HMS-PP, a biaxially stretchedpolypropylene film having high stiffness in the longitudinal direction,which has previously been difficult to manufacture by a publicly knownlongitudinal-transverse sequential biaxial stretching, can bemanufactured. In other words, the HMS-PP described above prevents thelongitudinally-oriented crystals from re-orienting in the transversedirection during transverse stretching.

[0178] Preferable examples of methods for preparing the above-describedHMS-PP include a method whereby a polypropylene containing a largeamount of high-molecular-weight components is blended, a method wherebypolymer or oligomer having a branch structure is blended, a methoddisclosed in Japanese Unexamined Patent Application Publication No.62-121704 whereby a long-chain branched structure is introduced into apolypropylene molecule, and a method disclosed in Japanese PatentPublication No. 2869606 in which a straight-chain crystallinepolypropylene, which has a melt strength, a inherent viscosity, acrystallization temperature, and a melting point that satisfy apredetermined formula and exhibits a boiling-xylene extraction residualrate within a predetermined range, is prepared without introducinglong-chain branches.

[0179] Among them, the biaxially stretched polypropylene film of thefifth embodiment of the present invention preferably comprises a HMS-PPthe melt strength of which is increased by introducing long-chainbranches into polypropylene molecules. Specific examples of the HMS-PPthe melt strength of which is increased by introducing a long-chainbranch include HMS-PP (Type name: PF-814, etc.) manufactured by BasellPolyolefins, HMS-PP (Type name: WB130HMS, etc.) manufactured byBorealis, and HMS-PP (Type name: D201, etc.) manufactured by DowChemical Company, etc.

[0180] An example of an index indicating the degree of long-chainbranching in the polypropylene is a branching index g represented by theequation below:

g=[η]_(LB)/[η]_(Lin)

[0181] wherein [η]_(LB) is the intrinsic viscosity of the polypropylenehaving a long-chain branch, and [η]_(Lin) is the intrinsic viscosity ofa straight-chain crystalline polypropylene having substantially the sameweight average molecular weight as the polypropylene having thelong-chain branch. The intrinsic viscosity is measured by a publiclyknown method in which a sample dissolved in tetralin is measured at 135°C. The weight average molecular weight is measured by a method presentedby M. L. McConnell in American Laboratory, May 63-75 (1978), i.e.,low-angle laser light scattering photometry.

[0182] The branching index g of the HMS-PP comprised in the biaxiallystretched polypropylene film of the fifth embodiment of the presentinvention is preferably 0.95 or less, and more preferably, 0.9 or less.If a branching index exceeds 0.95, the effect of adding the HMS-PP maybe diminished, resulting in insufficient Young's modulus in thelongitudinal direction when processed into a film.

[0183] The melt strength (MS) of the HMS-PP comprised in the biaxiallystretched polypropylene film of the fifth embodiment of the presentinvention is preferably in the range of 3 to 100 cN. If a MS is lessthan 3 cN, the Young's modulus in the longitudinal direction of theresulting film may be insufficient. The Young's modulus in thelongitudinal direction tends to increase as the melt strength (MS)becomes larger; however, if a melt strength (MS) exceeds 100 cN, filmformability may be degraded. More preferably, the melt strength (MS) ofthe HMS-PP is in the range of 4 to 80 cN, more preferably, 5 to 40 cN,and furthermore preferably 5 to 20 cN.

[0184] The content of the HMS-PP comprised in the polypropylene used inthe biaxially stretched polypropylene film of the fifth embodiment ofthe present invention is not restricted. However, the HMS-PP content ispreferably 1 to 60 percent by weight. A certain degree of effect can beachieved with a relatively small content. If a HMS-PP content is lessthan 1 percent by weight, the stretchability in the transverse directionmay be degraded, and improvements in the stiffness in the longitudinaldirection may be small. If a HMS-PP content exceeds 60 percent byweight, the stretchability in the longitudinal direction, the impactresistance, and the haze of the resulting film may be degraded. Morepreferably, the HMS-PP content is in the range of 2 to 50 percent byweight, and furthermore preferably, 3 to 40 percent by weight.

[0185] The melt strength (MS) and the melt flow rate (MFR) measured at230° C. of the polypropylene used in the biaxially stretchedpolypropylene film of the fifth embodiment of the present inventionpreferably satisfy the formula:

log(MS)>−0.61 log(MFR)+0.52

[0186] More preferably, the polypropylene used in the present inventionsatisfies the formula:

log(MS)>−0.61 log(MFR)+0.56

[0187] Particularly preferably, the relationship formula below issatisfied:

log(MS)>−0.61 log(MFR)+0.62

[0188] The melt strength and the melt flow rate can be controlled byadjusting the amount of the HMS-PP described above. The stiffness in thelongitudinal direction can be further increased.

[0189] For example, the polypropylene satisfying the formula

log(MS)>−0.61 log(MFR)+0.52

[0190] can be prepared by blending, a high-melt-strength polypropylene(HMS-PP) having a high melt strength with a conventional polypropylene,and by introducing long-chain branch components into the main-chain ofthe conventional polypropylene by means of copolymerization or graftpolymerization, so as to increase the melt strength (MS) of thepolypropylene. With the HMS-PP, the longitudinally-oriented crystals areprevented from being re-oriented in the transverse direction duringtransverse stretching.

[0191] The Trouton ratio of the polypropylene used in the biaxiallystretched polypropylene film of the fifth embodiment of the presentinvention is preferably 16 or more.

[0192] Generally, the Trouton ratio of the polypropylene used in thebiaxially stretched polypropylene film of the fifth embodiment of thepresent invention is preferably high. However, at an excessively highratio, the film formability and the surface haze may be degraded. TheTrouton ratio is more preferably 18 or more, more preferably in therange of 20 to 50, and most preferably in the range of 20 to 45. TheTrouton ratio can be controlled by adjusting the amount of addition ofHMS-PP described above, and the stiffness in the longitudinal directioncan be further increased.

[0193] Examples of methods for preparing the polypropylene having aTrouton ratio of 16 or more include a method in which a HMS-PP having aTrouton ratio of 30 or more is blended with a conventional polypropyleneand a method in which long-chain branch components are introduced intothe main chains of a conventional polypropylene by means ofcopolymerization or graft polymerization so as to increase the meltstrength (MS) of the polypropylene. With the HMSPP, thelongitudinally-oriented crystals are prevented from re-orienting in thetransverse direction during the transverse stretching.

[0194] The melt flow rate (MFR) of the polypropylene used in thebiaxially stretched polypropylene film of the fifth embodiment of thepresent invention is preferably in the range of 1 to 30 g/10 min fromthe point of view of the film formability. If a melt flow rate (MFR) isless than 1 g/10 min, problems such as an increase in filtrationpressure during melt extrusion and an increase in time required forreplacing extrusion materials may occur. If a melt flow rate (MFR)exceeds 30 g /10 min, the thickness irregularity in the resulting filmmay be large, which is a problem. The melt flow rate (MFR) is morepreferably 1 to 20 g/10 min.

[0195] The meso pentad fraction (mmmm) of the polypropylene used in thebiaxially stretched polypropylene film of the fifth embodiment of thepresent invention is preferably in 90 to 99.5%, and more preferably, 94to 99.5%. Here, the meso pentad fraction (mmmm) is the index thatdirectly indicates the conformation of isotactic stereo-regularity inpolypropylene. If a meso pentad fraction (mmmm) is 90 to 99.5%, a filmhaving superior dimensional stability, heat resistance, stiffness,moisture-proof property, and chemical resistance can be reliablymanufactured. Thus, a film that exhibits high converting ability duringfilm converting processes such as printing, coating, metallizing,bag-making, and laminating can be manufactured. If a meso pentadfraction (mmmm) is less than 90%, the resulting film tends to exhibit aless stiffness and a large heat shrinkage, which may result indegradation in converting ability during film converting such asprinting, coating, metallization, bag-making, and laminating, and in anincrease in high water vapor permeability. If a meso pentad fraction(mmmm) exceeds 99.5%, the film formability may be degraded. Morepreferably, the meso pentad fraction (mmmm) is 95 to 99%, andfurthermore preferably, 96 to 98.5%.

[0196] The isotactic index (II) of the polypropylene used in thebiaxially stretched polypropylene film of the fifth embodiment of thepresent invention is preferably in the range of 92 to 99.8%. At anisotactic index (II) of less than 92%, the resulting film may exhibit aless stiffness, a large heat shrinkage, and may have a degradedmoisture-proof property, which are problems. If an isotactic index (II)exceeds 99.8%, the film formability may be degraded. The isotactic index(II) is more preferably in the range of 94 to 99.5%.

[0197] The polypropylene used in the biaxially stretched polypropylenefilm of the fifth embodiment of the present invention may be blendedwith scrapped films produced during manufacture of the biaxiallystretched polypropylene film of the present invention or scrapped filmsproduced during manufacture of other types of film or other types ofresins to improve economical efficiency as long as the characteristicsof the present invention are not degraded.

[0198] The polypropylene used in the biaxially stretched polypropylenefilm of the present invention mainly comprises homopolymers of thepropylene. The polypropylene may be a polymer in which monomercomponents of other unsaturated hydrocarbons are copolymerized or may beblended with polymers in which propylene is copolymerized with monomercomponents other than propylene, as long as the purpose of the presentinvention can be achieved. Examples of the copolymer components andmonomer components for preparing the blended material include ethylene,propylene (for preparing the copolymerized blended material), 1-butene,1-pentene, 3-methylpentene-1,3-methylbutene-1,1-hexene,4-methypentene-1,5-ethylhexene-1,1-octene, 1-decene, 1-dodecene,vinylcyclohexene, styrene, allylbenzene, cyclopentene, norbornene, and5-methyl-2-norbornene, etc.

[0199] The above-described characteristic values of the polypropylenesuch as the melt strength (MS), the melt flow rate (MFR), the Troutonratio, the g value, the meso pentad fraction (mmmm), and the isotacticindex (II) are preferably measured using raw material chips beforefilm-formation. Alternatively, after film-formation, the film may besubjected to extraction with n-heptane at 60° C. or less forapproximately 2 hours to remove impurities and additives and thenvacuum-dried at 130° C. for at least 2 hours to prepare a sample. Theabove-described values may be then measured using this sample.

[0200] In order to increase the strength and improve the filmformability, at least one additive that has compatibility with thepolypropylene and can provide plasticity during stretching is preferablycontained in the biaxially stretched polypropylene film of the fifthembodiment of the present invention. Here, the additive that can provideplasticity refers to a plasticizer that enables stable stretching to ahigh stretching ratio. Without the additive, the purpose of the presentinvention is not sufficiently achieved, sufficient longitudinal fibrilscannot be obtained, and the film formability is degraded. The additiveis preferably at least one of petroleum resins substantially containingno polar groups and/or terpene resins substantially containing no polargroups from the point of view of achieving stretching to a high ratioand improved barrier property.

[0201] The petroleum resins substantially containing no polar grouprefers to petroleum resins containing no polar groups such as hydroxyl,carboxyl, halogen, or sulfone, or modified forms thereof. Specificexamples of the resins are cyclopentadiene resins made from petroleumunsaturated hydrocarbon and resins containing higher olefin hydrocarbonas the primary component.

[0202] Preferably, the glass transition temperature (hereinafter,sometimes referred to as Tg) of the petroleum resin substantiallycontaining no polar group is 60° C. or more. If a glass transitiontemperature (Tg) is less than 60° C., the effect of improving thestiffness may be small.

[0203] Particularly preferably, a hydrogen-added (hereinafter, sometimesreferred to as hydrogenated) petroleum resin, whose hydrogenation rateis 90% or more and more preferably 99% or more, is used. Arepresentative example of the hydrogen-added petroleum resin is analicyclic petroleum resin such as polydicyclopentadiene having a glasstransition temperature (Tg) of 70° C. or more and a hydrogenation rateof 99% or more.

[0204] Examples of the terpene resins substantially containing no polargroup are terpene resins containing no polar group such as hydroxyl,aldehyde, ketone, carboxyl, halogen, or sulfone, or the modified formsthereof, etc., i.e., hydrocarbons represented by (C₅H₈)n and modifiedcompounds derived therefrom, wherein n is a natural number between 2 and20.

[0205] The terpene resins are sometimes called terpenoids.Representative compounds thereof include pinene, dipentene, carene,myrcene, ocimene, limonene, terpinolene, terpinene, sabinene,tricyclene, bisabolene, zingiberene, santalene, campholene, mirene, andtotarene, etc. In relation to the biaxially stretched polypropylene filmof the present invention, hydrogen is preferably added at hydrogenationrate of 90% or more, particularly preferably, 99% or more. Among them,hydrogenated β-pinene and hydrogenated β-dipentene are particularlypreferred.

[0206] The bromine number of the petroleum resin or the terpene resin ispreferably 10 or less, more preferably 5 or less, and most preferably 1or less.

[0207] The amount of the additive may be large enough to achieve theplasticizing effect. Preferably, the total amount of the petroleum resinand the terpene resin is in the range of 0.1 to 30 percent by weight.When the amount of the additive resins is less than 0.1 percent byweight, the effect of improving the stretchability and the stiffness inthe longitudinal direction may become small and the transparency may bedegraded. When an amount exceeds 30 percent by weight, thermaldimensional stability may be degraded, and the additive may bleed outonto the film surface, resulting in degradation of slipperiness. Theamount of additives or the total amount of the petroleum resin and theterpene resin is more preferably 1 to 20 percent by weight, andfurthermore preferably 2 to 15 percent by weight.

[0208] When a petroleum resin and/or a terpene resin that contain polargroups is used as the additive, voids may readily be formed inside thefilm, the water vapor permeability may increase, and bleeding out ofantistatic agents or lubricants may be prevented due to their poorcompatibility with polypropylene.

[0209] Specific examples of additives that are compatible with thepolypropylene and can provide plasticizing effect during stretchinginclude “Escorez” (type name: E5300 series, etc.) manufactured by TornexCo., “Clearon” (type name: P-125, etc.) manufactured by YasuharaChemical Co., Ltd., and “Arkon” (type name: P-125, etc.) manufactured byArakawa Chemical Industries, Ltd, etc.

[0210] The biaxially stretched polypropylene film of the fifthembodiment of the present invention can be made into a metallized filmhaving a high gas barrier property by depositing a metallization layeron at least one side of the film.

[0211] Moreover, at least one side of the biaxially stretchedpolypropylene film of the fifth embodiment of the present invention maybe provided with a coating layer composed of polyesterpolyurethane-basedresin and a metallization layer. As a result, a metallized film having asuperior gas barrier property to that of the above-described metallizedfilm can be made.

[0212] In achieving high gas barrier property after metallization, thecoating layer is preferably formed by applying a blended coatingmaterial containing a water-soluble organic solvent and a water-solubleand/or water-dispersible crosslinked polyesterpolyurethane-based resin,and drying the applied coat.

[0213] The polyesterpolyurethane-based resin used in the coating layerincludes polyester-polyol obtained by esterifying dicarboxylic acid anda diol component, and polyisocyanate. A chain extension agent may beincluded, if necessary.

[0214] Examples of the dicarboxylic acid component in thepolyesterpolyurethane-based resin used in the coating layer includeterephthalic acid, isophthalic acid, 2,6-naphthalene dicarboxylic acid,adipic acid, trimethyladipic acid, sebacic acid, malonic acid,dimethylmalonic acid, succinic acid, glutaric acid, pimelic acid,2,2-dimethylglutaric acid, azelaic acid, fumaric acid, maleic acid,itaconic acid, 1,3-cyclopentane dicarboxylic acid, 1,2-cyclohexanedicarboxylic acid, 1,4-cyclohexane dicarboxylic acid, 1,4-naphthalicacid, diphenic acid, 4,4′-hydroxybenzoic acid, and 2,5-naphthalenedicarboxylic acid, etc.

[0215] Examples of the diol component in the polyesterpolyurethane-basedresin used in the coating layer include aliphatic glycols such asethylene glycol, 1,4-butanediol, diethylene glycol, and triethyleneglycol; aromatic diols such as 1,4-cyclohexane dimethanol; andpoly(oxyalkylene)glycols such as polyethylene glycol, polypropyleneglycol, and polytetramethylene glycol, etc.

[0216] The polyesterpolyurethane-based resin used in the coating layermay be copolymerized with hydroxy-carboxylic acid, etc. such asp-hydroxy benzoic acid, etc. in addition to containing the dicarboxylicacid component and the diol component. Moreover, although these have alinear structure, branching polyester may be made using ester-formingcomponents of trivalent or more.

[0217] Examples of polyisocyanate include hexamethylene diisocyanate,diphenylmethane diisocyanate, tolylene diisocyanate, isophoronediisocyanate, tetramethylene diisocyanate, xylylene diisocyanate, lysinediisocyanate, an adduct of tolylene diisocyanate and trimethylolpropane,and an adduct of hexamethylene diisocyanate and trimethylolethane, etc.

[0218] Examples of the chain extension agent includependant-carboxyl-group-containing diols; glycols such as ethyleneglycol, diethylene glycol, propylene glycol, 1,4-butanediol,hexamethylene glycol, and neopentyl glycol; and diamines such asethylenediamine, propylenediamine, hexamethylenediamine,phenylenediamine, tolylenediamine, diphenyldiamine,diaminodiphenylmethane, diaminodiphenylmethane, anddiaminocyclohexylmethane, etc.

[0219] A specific example of the polyesterpolyurethane-based resinincludes “Hydran” (type name: AP-40F, etc.) manufactured by DainipponInk and Chemicals, Inc., etc.

[0220] In forming the coating layer, at least one ofN-methylpyrrolidone, ethylcellosolve acetate, and dimethylformamide aswater-soluble organic solvents is preferably added to the coatingmaterial to improve the coating-layer formability and increase theadhesion of the coating layer to the base layer. Particularly,N-methylpyrrolidone is preferred since it has a significant effect ofimproving the coating-layer formability and increasing the adhesion ofthe coating layer to the base layer. Preferably, the content of thewater-soluble organic solvent is 1 to 15 parts by weight, and morepreferably 3 to 10 parts by weight relative to 100 parts by weight ofthe polyesterpolyurethane-based resin from the point of view offlammability of the coating material and odor control.

[0221] Preferably, a crosslinking structure is introduced into thewater-dispersible polyesterpolyurethane-based resin so as to increasethe adhesion between the coating layer and the base layer. Examples ofthe method for obtaining such a coating material include methodsdisclosed in Japanese Unexamined Patent Application Publication Nos.63-15816, 63-256651, and 5-152159. At least one crosslinking agentselected from isocyanate compounds, epoxy compounds, and amine compoundsis added as the crosslinking component. These crosslinking agents formcrosslinks with the polyesterpolyurethane-based resin described aboveand thus increase the adhesion between the base layer and themetallization layer.

[0222] Examples of the isocyanate compounds used as the crosslinkingagents include toluene diisocyanate, xylene diisocyanate, naphthalenediisocyanate, hexamethylene diisocyanate, and isophorone diisocyanate,etc., described above. However, it is not limited to these isocyanatecompounds.

[0223] Examples of the epoxy compounds used as the crosslinking agentsinclude diglycidyl ether of bisphenol A and oligomers thereof,diglycidyl ether of hydrogenated bisphenol A and oligomers thereof,diglycidyl ether orthophthalate, diglycidyl ether isophthalate,diglycidyl ether terephthalate, and diglycidyl ether adipate, etc.However, it is not limited to these epoxy compounds.

[0224] Examples of the amine compounds used as the crosslinking agentsinclude amine compounds such as melamine, urine, benzoguanamine, etc.;amino resins obtained by addition condensation of the above-describedamino compounds with formaldehyde or C₁-C₆ alcohol;hexamethylenediamine; and triethanolamine, etc. However, it is notlimited to these amine compounds.

[0225] An amine compound is preferably contained in the coating layerfrom the point of view of food hygiene and adhesion to the basematerial. A specific example of the amine compound used as thecrosslinking agent is “Beckamine” (type name: APM, etc.) manufactured byDainippon Ink and Chemicals, Inc., etc.

[0226] The amount of the crosslinking agent selected from isocyanatecompounds, epoxy compounds, and amine compounds is preferably 1 to 15parts by weight, and more preferably 3 to 10 parts by weight relative to100 parts by weight of the mixed coating material of the water-solublepolyesterpolyurethane-based resin and the water-soluble organic solventfrom the point of view of improving the chemical resistance andpreventing degradation in the water-proof property. When the amount ofthe crosslinking agent is less than above-described range, the effect ofimproving the adhesion may not be obtained. At an amount exceeding 15parts by weight, the adhesion between the coating layer and the baselayer may be degraded presumably due to the unreacted remainingcrosslinking agent.

[0227] Moreover, a small amount of a crosslinking accelerator may beadded to the coating layer so that the coating layer compositiondescribed above can completely form crosslinks and cure within a timetaken to manufacture a film for metallization.

[0228] The crosslinking accelerator contained in the coating layer ispreferably a water-soluble acidic compound since it has a significantcrosslinking promoting effect. Examples of the crosslinking acceleratorinclude terephthalic acid, isophthalic acid, 2,6-naphthalenedicarboxylic acid, adipic acid, trimethyladipic acid, sebacic acid,malonic acid, dimethylmalonic acid, succinic acid, glutaric acid,sulfonic acid, pimelic acid, 2,2-dimethylglutaric acid, azelaic acid,fumaric acid, maleic acid, itaconic acid, 1,3-cyclopentane dicarboxylicacid, 1,2-cyclohexane dicarboxylic acid, 1,4-cyclohexane dicarboxylicacid, 1,4-naphthalic acid, diphenic acid, 4,4′-hydroxy benzoic acid, and2,5-naphthalene dicarboxylic acid, etc.

[0229] A specific example of the crosslinking accelerator is “Catalyst”(type name: PTS, etc.) manufactured by Dainippon Ink and Chemicals,Inc., etc.

[0230] Moreover, inert particles may be added to the coating layer.Examples of the inert particles include inorganic fillers such assilica, alumina, calcium carbonate, barium sulfate, magnesium oxide,zinc oxide, and titanium oxide, and organic polymer particles such ascrosslinked-polystyrene particles, crosslinked-acryl particles, andcrosslinked-silicon particles, etc. In addition to the inert particles,a wax-based lubricant and a mixture of these, etc. may be added.

[0231] The coating layer is preferably formed on at least one side ofthe base layer at a thickness of 0.05 to 2 μm. When the thickness of thecoating layer is less than 0.05 μm, the adhesion to the base layer isdecreased, and coating defect may be formed, resulting in degradation ofthe gas barrier property after metallization. When the thickness of thecoating layer exceeds 2 μm, the time required for curing of the coatinglayer becomes longer, and the crosslinking reaction described above maybe incomplete, thereby degrading the gas barrier property. Moreover,when the coating layer is formed on the base layer during thefilm-forming process, the reclaimability of the film scraps to the baselayer is degraded, and numerous inner voids are formed by the resin ofthe coating layer which acts as the nuclei, thereby degrading themechanical properties.

[0232] The adhesive strength between the coating layer and the baselayer is preferably 0.6 N/cm or more. When the adhesive strength betweenthe coating layer and the base layer is less than 0.6 N/cm, the coatinglayer may peel off during converting, thereby imposing a significantlylarge limitation on the usage. The adhesive strength between the coatinglayer and the base layer is preferably 0.8 N/cm or more, and morepreferably 1.0 N/cm or more.

[0233] When a coating layer is formed on at least one side of thebiaxially stretched polypropylene film of the fifth embodiment of thepresent invention so that the film can be used as the film formetallization, the centerline average roughness (Ra) of the biaxiallystretched polypropylene film of the fifth embodiment of the presentinvention is preferably 0.01 to 0.5 μm from the point of view ofhandling convenience, slipperiness, and blocking prevention. Morepreferably, the centerline average roughness is 0.02 to 0.2 μm. When thecenterline average roughness (Ra) is less than 0.02 μm, the slipperinessmay be degraded, resulting in the degradation of handling convenience ofthe film. At a centerline average roughness (Ra) exceeding 0.2 μm,pinholes may occur in an aluminum layer when a metallized film is madeby sequentially depositing the coating layer and a metallization layer,thereby degrading the gas barrier property.

[0234] When a coating layer is formed on at least one side of thebiaxially stretched polypropylene film of the fifth embodiment of thepresent invention so that the film can be used as the film formetallization, the surface gloss of the biaxially stretchedpolypropylene film of the fifth embodiment of the present invention ispreferably 135% or more, and more preferably 138% or more to ensuresuperior metallic gloss after metallization.

[0235] In the present invention, the coating layer is preferably formedby a process of applying a coating solution using a reverse roll coater,a gravure coater, a rod coater, an air doctor coater, or other coatingmachines outside the polypropylene film manufacturing process. Morepreferably, the coating is performed in the film manufacturing process.More preferably, examples thereof include a method to apply coatingsolutions during the film manufacturing process, in which a coatingsolution is applied on an unstretched polypropylene film and then thefilm is sequentially biaxially stretched, and in which a coatingsolution is applied on a uniaxially stretched polypropylene film andthen the film is stretched in the direction perpendicular to theuniaxial stretching. This method in which a coating solution is appliedon a uniaxially stretched polypropylene film and then stretching thefilm in the direction perpendicular to the uniaxial stretching is mostpreferred since the thickness of the coating layer can be uniform andthe production efficiency can be improved.

[0236] When the biaxially stretched polypropylene film of the fifthembodiment of the present invention is used as the film formetallization, the polypropylene used in the base layer preferablycontains no organic lubricants such as fatty acid amide, etc. in pointof view of adhesion of the coating layer and the metallization layer.However, a small amount of organic crosslinked particles or inorganicparticles may be added to provide slipperiness and improve theprocessability and windability. Examples of the organic crosslinkedparticles added to the polypropylene of the base layer at a small amountinclude crosslinked-silicone particles,crosslinked-polymethylmethacrylate particles, andcrosslinked-polystyrene particles, etc. Examples of the inorganicparticles include zeolite, calcium carbonate, silicon oxide, andaluminum silicate, etc. The average particle size of these particles ispreferably 0.5 to 5 μm since the slipperiness can be increased withoutsignificantly degrading the transparency of the film of the presentinvention.

[0237] An antistatic agent for avoiding the troubles resulting from thestatic electrification of the film is preferably added to the biaxiallystretched polypropylene film of the fifth embodiment of the presentinvention except for when the film is used as the film for metallizationhaving the above-described construction. The antistatic agent containedin the biaxially stretched polypropylene film of the fifth embodiment ofthe present invention is not restricted. However, examples of theantistatic agent include ethylene oxide adducts of betaine derivatives,quaternary amine compounds, alkyldiethanolamine fatty acid esters,glycerin fatty acid ester, gylceride stearates, etc. and mixtures ofthese.

[0238] A lubricant is preferably added, more preferably, in addition tothe antistatic agent described above except for when the film is used asthe film for metallization having the above-described construction. Thelubricant is added to improve the mould-releasing property and theflowability during thermo-forming of thermoplastic resins according tothe wordings of Japanese Industrial Standards, and to adjust thefrictional force between a converting machine and the film surface andbetween the films themselves.

[0239] The lubricant is not restricted. However, examples of thelubricants include amide compounds such as stearamide, erucic amide,erucamide, oleamide, etc. and mixtures of these.

[0240] The content of the antistatic agent is preferably 0.3 parts byweight or more, and more preferably in the range of 0.4 to 1.5 parts byweight relative to 100 parts by weight of the polypropylene resin used.The total content of the antistatic agent and the lubricant is morepreferably 0.5 to 2.0 parts by weight from the point of view ofantistatic property and slipperiness.

[0241] Inorganic particles and/or crosslinked organic particles forincreasing the slipperiness are preferably contained in the biaxiallystretched polypropylene film of the fifth embodiment of the presentinvention.

[0242] In the present invention, the term “inorganic particles” refersto inorganic particles of metal compounds, and the inorganic particle isnot restricted. However, examples of inorganic particles includeinorganic particles of zeolite, calcium carbonate, magnesium carbonate,alumina, silica, aluminum silicate, kaolin, kaolinite, talc, clay,diatomite, montmorillonite, and titanium oxide, etc. and mixtures ofthese.

[0243] In the present invention, the term “crosslinked organicparticles” refers to particles in which polymer compounds arecrosslinked by a crosslinking agent. The crosslinked organic particlescontained in the biaxially stretched polypropylene film of the presentinvention are not restricted. However, examples of crosslinked organicparticles include crosslinked particles of polymethoxysilane-basedcompounds, crosslinked particles of polystyrene-based compounds,crosslinked particles of acrylic-based compounds, crosslinked particlesof polyurethane-based compounds, crosslinked particles ofpolyester-based compounds, crosslinked particles of fluoric-basedcompounds, and mixtures of these.

[0244] The average particle size of the inorganic particles andcrosslinked organic particles is preferably in the range of 0.5 to 6 μm.If an average particle size of is less than 0.5 μm, the slipperiness maybe degraded. If an average particle size exceeds 6 μm, drop-off ofparticles may occur, and the film surface may be readily damaged whenthe films come into contact with each other.

[0245] The amount of the inorganic particles and/or the crosslinkedorganic particles added is preferably in the range of 0.02 to 0.5percent by weight, and more preferably 0.05 to 0.2 percent by weightfrom the point of view of blocking prevention, slipperiness, andtransparency.

[0246] In addition to the above-described additives, a nucleating agent,a heat stabilizer, and an antioxidant may be added to the biaxiallystretched polypropylene film of the fifth embodiment of the presentinvention, if necessary.

[0247] Examples of the nucleating agent include sorbitol-based,organic-metal-phosphate-ester-based, organic-metalcarboxylate-based, androsin-based nucleating agents. The amount of the nucleating agent is 0.5percent by weight or less. As the heat stabilizer,2,6-di-tertiary-butyl-4-methylphenol (BHT) or the like may be added inamount of 0.5 percent by weight or less. As the antioxidant,tetrakis-(methylene-(3,5-di-tertiary-butyl-4-hydroxy-hydrocinnamate))butane(Irganox 1010) or the like may be added in amount of 0.5 percent byweight or less.

[0248] A publicly known polyolefin resin is preferably laminated on atleast one side of the biaxially stretched polypropylene film of thefifth embodiment of the present invention for the purposes other thanthose described above, such as prevention of bleed-out/flying-off ofadditives, adhesion of the metallization layer, high printability,enhancement of heat sealability, enhancement of printlaminationproperty, enhancement of glossy appearance, haze reduction (enhancementof transparency), enhancement of releasing property, and enhancement ofslipperiness, etc.

[0249] The thickness of the laminated polyolefin resin is preferably0.25 μm or more and half the total thickness of the film or less. If athickness is less than 0.25 μm, it is difficult to form a uniform layerdue to lamination defects. When the thickness exceeds half the totalthickness of the film, the effect of the surface layer on the mechanicalproperty becomes large, resulting in a decrease in Young's modulus andtension resistance of the film. This resin laminated on the surface neednot satisfy the ranges of the present invention. Examples of thelamination method include co-extrusion, in-line/off-line extrusionlamination and in-line/off-line coating, etc. The method is not limitedto these, and the most suitable method should be selected as needed.

[0250] At least one film surface of the biaxially stretchedpolypropylene film of the fifth embodiment of the present invention ispreferably subjected to corona discharge treatment so as to allow thefilm surface to have a surface wetting tension of at least 35 mN/mbecause the printability, adhesion, antistatic property, and lubricantbleed-out property can be improved. The atmospheric gas during coronadischarge treatment is preferably air, oxygen, nitrogen, carbon dioxidegas, or a nitrogen/carbon dioxide mixture gas. From the point of view ofeconomical efficiency, corona discharge treatment in air is particularlypreferred.

[0251] The Young's modulus in the longitudinal direction (Y(MD)) at 25°C. of the biaxially stretched polypropylene film of the fifth embodimentof the present invention is preferably 2.5 GPa or more. When the Y(MD)at 25° C. is less than 2.5 GPa, the stiffness in the transversedirection becomes high when compared with that in the longitudinaldirection, resulting in an imbalance of stiffness and insufficientfirmness of the film. As a result, the film may exhibit insufficienttension resistance. The Young's modulus in the longitudinal direction(Y(MD)) at 25° C. can be controlled by adjusting the temperature ofcooling drum for cooling and solidifying the molten material to preparean unstretched sheet, the conditions for the longitudinal stretching(temperature, stretching ratio, etc.), the crystallinity of thepolypropylene (depending on meso pentad fraction (mmmm), isotactic index(II), etc.), the amount of the additive for providing plasticity duringstretching, and the like. The optimum film forming conditions and rawmaterials should be selected as needed, as long as the advantages of thepresent invention are not impaired. The Young modulus in thelongitudinal direction (Y(MD)) at 25° C. is more preferably 2.7 GPa ormore, yet more preferably 3.0 GPa or more, and most preferably 3.2 GPaor more.

[0252] The Young's modulus in the longitudinal direction (Y(MD)) at 80°C. of the biaxially stretched polypropylene film of the fifth embodimentof the present invention is preferably 0.4 GPa or more. When the Y(MD)at 80° C. is less than 0.4 GPa, the tension resistance during filmconverting may be insufficient. The Young's modulus (Y(MD)) in thelongitudinal direction at 80° C. can be controlled by adjusting thetemperature of cooling drum for cooling and solidifying the moltenmaterial to prepare an unstretched sheet, the conditions for thelongitudinal stretching (temperature, stretching ratio, etc.), thecrystallinity of the polypropylene (depending on meso pentad fraction(mmmm), isotactic index (II), etc.), the amount of the additive forproviding plasticity during stretching, and the like. The optimum filmforming conditions and raw materials should be selected as needed, aslong as the advantages of the present invention are not impaired. TheYoung's modulus in the longitudinal direction (Y(MD)) at 80° C. is morepreferably 0.5 GPa or more, and furthermore preferably 0.6 GPa or more.

[0253] In the biaxially stretched polypropylene film of the fifthembodiment of the present invention, the m value at 25° C. is preferablyin the range of 0.4 to 0.7 wherein the m value in terms of a Young'smodulus in the longitudinal direction (Y(MD)) and a Young's modulus inthe transverse direction (Y(TD)) is expressed as below:

m=Y(MD)/(Y(MD)+Y(TD))

[0254] Here, the m value is the ratio of the Young's modulus in thelongitudinal direction to the total of the Young's moduli in thelongitudinal and transverse directions. Accordingly, a film having an mvalue of less than 0.5 has a higher stiffness in the transversedirection than in the longitudinal direction. A film having an m valueof 0.5 has a substantially balanced stiffness between the stiffness inthe longitudinal direction and the stiffness in the transversedirection. A film having an m value of more than 0.5 has a higherstiffness in the longitudinal direction than in the transversedirection. When a film has an m value of 0.4 to 0.7, the film hasbalanced and high stiffness. When the m value at 25° C. is less than0.4, the stiffness in the longitudinal direction is significantly lowerthan that in the transverse direction, resulting in an imbalance of thestiffness. This may result in insufficient tension resistance duringfilm converting and insufficient film stiffness and is therefore notpreferred. An m value exceeding 0.7 is also not preferred since thestiffness in the transverse direction may be significantly lower thanthat in the longitudinal direction and the firmness of the resultingfilm may be insufficient.

[0255] The m value at 25° C. can be controlled by adjusting thefilm-forming conditions, e.g., the temperature of cooling drum forcooling and solidifying the molten material to prepare an unstretchedsheet, the temperatures during longitudinal/transverse stretching,stretching ratio, relaxation of the film after longitudinal/transversestretching; the crystallinity of the polypropylene (depending on mesopentad fraction (mmmm), isotactic index (II), etc.): the amount of theadditive for providing plasticity during stretching, and the like. Theoptimum film-forming conditions and raw materials should be selected asneeded, as long as the advantages of the present invention are notimpaired. The m value at 25° C. is more preferably 0.42 to 0.68, yetmore preferably 0.44 to 0.65, and most preferably 0.46 to 0.62.Preferably, the m value at 80° C. is also in the range of 0.4 to 0.7.

[0256] The F2 value in the longitudinal direction at 25° C. of thebiaxially stretched polypropylene film of the fifth embodiment of thepresent invention is preferably 40 MPa or more. Here, the F2 value inthe longitudinal direction is a stress applied on a sample 15 cm in thelongitudinal direction and 1 cm in the transverse direction at anelongation of 2% when the sample is stretched at an original length of50 mm and a testing speed of 300 mm/min. When the F2 value in thelongitudinal direction at 25° C. is less than 40 MPa, the stiffness inthe transverse direction becomes higher than that in the longitudinaldirection, resulting in a film having an imbalanced stiffness and lowfirmness. Moreover, the tension resistance of the film may be poor. TheF2 value is more preferably 45 MPa in the longitudinal direction at 25°C. or more.

[0257] The F5 value in the longitudinal direction at 25° C. of thebiaxially stretched polypropylene film of the fifth embodiment of thepresent invention is preferably 50 MPa or more. Here, the F5 value inthe longitudinal direction is a stress applied on a sample 15 cm in thelongitudinal direction and 1 cm in the transverse direction at anelongation of 5% when the sample is stretched at an original length of50 mm and a testing speed of 300 mm/min. When the F5 value in thelongitudinal direction at 25° C. is less than 50 MPa, the stiffness inthe transverse direction becomes higher than that in the longitudinaldirection, resulting in a film having an imbalanced stiffness and lowfirmness. Moreover, the tension resistance of the film may be poor. TheF5 value in the longitudinal direction at 25° C. is more preferably 55MPa or more.

[0258] The heat shrinkage in the longitudinal direction (S(MD)) at 120°C. of the biaxially stretched polypropylene film of the fifth embodimentof the present invention is preferably 5% or less. When the heatshrinkage in the longitudinal direction at 120° C. exceeds 5%, anextensive degree of shrinking occurs when the film is heated duringprocesses such as printing, laminating, coating, metallizing, and thelike, resulting in process failures such as defects in the film, pitchdisplacement, and wrinkles. The heat shrinkage in the longitudinaldirection at 120° C. can be controlled by adjusting the temperature ofcooling drum for cooling and solidifying the molten material to preparean unstretched sheet, the conditions for the longitudinal stretching(stretching temperature, stretching ratio, relaxation of the film afterlongitudinal stretching, etc.), the crystallinity of the polypropylene(depending on meso pentad fraction (mmmm), isotactic index (II), etc.),the amount of the additive for providing plasticity during stretching,and the like. The optimum longitudinal-stretching conditions and rawmaterials should be selected as needed, as long as the advantages of thepresent invention are not impaired. More preferably, the heat shrinkagein the longitudinal direction at 120° C. is 4% or less.

[0259] In the biaxially stretched polypropylene film of the fifthembodiment of the present invention, the sum of the heat shrinkage inthe longitudinal direction (S(MD)) and the heat shrinkage in thetransverse direction at 120° C. is preferably 8% or less. When the sumof the heat shrinkage in the longitudinal and transverse directionsexceeds 8%, an extensive degree of shrinking occurs when the film isheated during processes such as printing, laminating, coating,metallizing, and the like, resulting in process failures such as defectsin the film, pitch displacement, and the like. The index (II) of thefifth embodiment corresponds to this. The sum of the heat shrinkages inthe longitudinal and transverse directions can be controlled byadjusting the amount of the additive for providing plasticity duringstretching and the like. The optimum film-forming conditions and rawmaterials should be selected as needed, as long as the advantages of thepresent invention are not impaired. More preferably, the sum of the heatshrinkage in the longitudinal (S(MD)) and the heat shrinkage in thetransverse directions at 120° C. is 6% or less.

[0260] The biaxially stretched polypropylene film of the presentinvention preferably has a Young's modulus in the longitudinal direction(Y(MD)) at 25° C. and a heat shrinkage in the longitudinal direction(S(MD)) at 120° C. that satisfy the formula below:

Y(MD)≧S(MD)−1

[0261] The biaxially stretched polypropylene film of the presentinvention that satisfies the above-described formula can exhibit hightension resistance and superior handling convenience during filmconverting. When the above-described formula is not satisfied, thebiaxially stretched polypropylene film may exhibit poor tensionresistance during film converting or may induce process failures due tofilm shrinkage. In order to satisfy the above-described formula,adjustment of the following may be performed: the film-formingconditions, e.g., the temperature of cooling drum for cooling andsolidifying the molten material to prepare an unstretched sheet, thetemperatures during longitudinal/transverse stretching, stretchingratio, relaxation of the film after longitudinal/transverse stretching;the crystallinity of the polypropylene (depending on meso pentadfraction (mmmm), isotactic index (II), etc.); the amount of the additivefor providing plasticity during stretching; and the like. The optimumfilm-forming conditions and raw materials should be selected as needed,as long as advantages of the present invention are not impaired. Morepreferably, the formula below is satisfied.

Y(MD)≧S(MD)−0.7

[0262] The water vapor permeability of the biaxially stretchedpolypropylene film of the fifth embodiment of the present invention ispreferably 1.5 g/m²/d/0.1 mm or less. When the water vapor permeabilityexceeds 1.5 g/m²/d/0.1 mm, the biaxially stretched polypropylene film ofthe present invention may exhibit poor moisture-proof property when itis used as a packaging material that shields the contents from theexternal air, for example. The water vapor permeability can becontrolled by adjusting the film-forming conditions, e.g., thetemperature of cooling drum for cooling and solidifying the moltenmaterial to prepare an unstretched sheet, the temperatures duringlongitudinal/transverse stretching, stretching ratio; the crystallinityof the polypropylene (depending on meso pentad fraction (mmmm),isotactic index (II), etc.); the amount of the additive for providingplasticity during stretching; and the like. The optimum film-formingconditions and raw materials should be selected as needed, as long asthe advantages of the present invention are not impaired. Morepreferably, the water vapor permeability is 1.2 g/m²/d/0.1 mm or less.

[0263] Publicly known methods may be employed in making the biaxiallystretched polypropylene film of the present invention. For example, apolypropylene which comprises a polypropylene satisfying the formulabelow,

log(MS)>−0.61 log(MFR)+0.82

[0264] or a polypropylene which consists of a polypropylene satisfyingthe formula below,

log(MS)>−0.61 log(MFR)+0.52

[0265] or a polypropylene a polypropylene which comprises having aTrouton ratio of 30 or more, or a polypropylene which consists of apolypropylene having a Trouton ratio of 16 or more is blended with atleast one of petroleum resins substantially containing no polar-groupand/or terpene resins substantially containing no polar-group, and themixture is fed into an extruder. The mixture is melted, filtered, andextruded from a slit die. The extruded mixture is then wound around acooling drum to be cooled and solidified into a sheet so as to make anunstretched film. The temperature of the cooling drum is preferably 20to 100° C. so that the film can be adequately crystallized. In thismanner, a large number of longitudinal fibrils having a large length canbe obtained after biaxially stretcing.

[0266] Next, the resulting unstretched film is biaxially stretched by apublicly known longitudinal-transverse sequential biaxial stretchingmethod. The important factor for making a biaxially stretchedpolypropylene film highly tensilized in the longitudinal direction isthe stretching ratio in the longitudinal direction. The reallongitudinal stretching ratio in a conventional longitudinal-transversesequential biaxial stretching method for manufacturing a polypropylenefilm is in the range of 4.5 to 5.5, and when a longitudinal stretchingratio exceeds 6, film-forming may become unstable, and the film maybreak during transverse stretching. On the contrary, in the presentinvention, the real longitudinal stretching ratio is preferably 6 ormore. When an real longitudinal stretching ratio is less than 6,sufficient longitudinal fibrils cannot be obtained, the stiffness in thelongitudinal direction of the film may be insufficient, and the firmnessof the resulting film may be insufficient in manufacturing thinner film.The more preferable real stretching ratio in the longitudinal directionis 7 or more, and the most preferable real stretching ratio is 8 ormore. It is sometimes preferable to perform the longitudinal stretchingin two or more steps from the point of view of tensilization in thelongitudinal direction and introduction of the longitudinal fibrils. Thelongitudinal stretching temperature is an optimum temperature selectedfrom the point of view of stability in film-forming, tensilization inthe longitudinal direction, and introduction of the longitudinalfibrils. The longitudinal stretching temperature is preferably 120 to150° C. Moreover, during the cooling process that follows longitudinalstretching, the film is preferably relaxed in the longitudinal directionto an extent that does not further induce thickness irregularity of thefilm from the point of view of dimensional stability in the longitudinaldirection.

[0267] The real stretching ratio in the transverse direction ispreferably 10 or less. When an real transverse stretching ratio exceeds10, the stiffness of the resulting film in the longitudinal directionmay be low, the number of longitudinal fibrils may decrease, and thefilm-forming may become unstable. The transverse stretching temperatureis an optimum temperature selected from the point of view of stabilityin film-forming, thickness irregularities, tensilization in thelongitudinal direction, and introduction of the longitudinal fibrils.The transversal stretching temperature is preferably 150 to 180° C.

[0268] After stretching in the transverse direction, the film isheat-set at 150 to 180° C. while relaxing the film in the transversedirection by 1% or more, cooled, and wound to obtain the biaxiallystretched polypropylene film of the present invention.

[0269] An example method for manufacturing a film for metallizationusing a biaxially stretched polypropylene film of the present inventionwill now be described. However, the present invention is not limited bythe manufacturing method described below.

[0270] For example, a polypropylene which comprises a polypropylenesatisfying the formula below:

log(MS)>−0.61 log(MFR)+0.82

[0271] or a polypropylene which consists of a polypropylene satisfyingthe formula below:

log(MS)>−0.61 log(MFR)+0.52

[0272] or a polypropylene which comprises a polypropylene having aTrouton ratio of 30 or more, or a polypropylene which consists of apolypropylene having a Trouton ratio of 16 or more is blended with atleast one of petroleum resins substantially containing no polar-groupand/or terpene resins substantially containing no polar-group. The mixedresin and/or the third layer resin is prepared. These resins are fedinto separate extruders, melted at 200 to 290° C., and are filtered. Theresins are put together inside a short pipe or a die, extruded from aslit die to form a laminate each layer of which has a target thickness,and wound around a cooling drum to be cooled and solidified into a sheetto obtain an unstretched laminate film. The temperature of the coolingdrum is preferably 20 to 90° C. so that the film can be adequatelycrystallized. In this manner, a large number of longitudinal fibrilshaving a large length can be obtained after biaxially stretcing.

[0273] The unstretched laminate film is heated to a temperature of 120to 150° C. and stretched in the longitudinal direction to 6 times theinitial length or more. The film is then fed into a tenter-type drawingmachine so as to stretch the film in the transverse direction to 10times the initial length or less at 150 to 180° C., relaxed by heatingat 150 to 180° C., and cooled. If necessary, a surface of the base layeron which a metallization layer is to be deposited and/or the third layersurface opposite of the base layer is subjected to corona dischargetreatment in air, nitrogen, or mixture gas of carbon dioxide andnitrogen. When a heat-seal layer is to be laminated as a third layer,corona discharge treatment is preferably avoided to achieve highadhesive strength. Next, the film is wound to obtain a biaxiallystretched polypropylene film for metallization.

[0274] To make a film having a superior gas barrier property, theabove-described unstretched laminate film is heated to a temperature of120 to 150° C., stretched in the longitudinal direction to 6 times theinitial length or more, and cooled. Subsequently, the above-describedcoating material is applied on the uniaxially stretched film base layer.The base layer surface may be subjected to corona discharge treatment,if necessary. The film is then fed into a tenter-type drawing machine,stretched at a temperature of 150 to 180° C. in the transverse directionto 10 times the initial length or less, relaxed by heating at 150 to180° C., and cooled. The resulting coating layer on the base layerand/or the third layer surface opposite of the base layer may besubjected to corona discharge treatment in air, nitrogen, or mixture gasof carbon dioxide and nitrogen if necessary. At this stage, when aheat-seal layer is to be laminated as a third layer, corona dischargetreatment is preferably avoided to achieve high adhesive strength. Next,the film is wound to obtain a biaxially stretched polypropylene film formetallization.

[0275] In the present invention, the biaxially stretched polypropylenefilm for metallization is preferably aged at 40 to 60° C. so as toaccelerate the reaction in the coating layer. When the reaction in thecoating layer is accelerated, the adhesive strength of the coating layerto the base layer and to the metallization layer can be increased, andgas barrier property of the film can be improved. Aging is preferablyperformed for 12 hours or more, and more preferably 24 hours or more toimprove the chemical resistance.

[0276] Next, the metallization is performed by vacuum metallization ofmetal. A metal from evaporation source is deposited on the coatinglayer, which coats the surface of the biaxially stretched polypropylenefilm of the present invention, to form a metallization layer.

[0277] Examples of the evaporation source include those of aresistance-heating boat type, a radiation- or radiofrequency-heatingcrucible type, and an electron beam heating type. The evaporation sourceis not restricted.

[0278] The metal used in the metallization is preferably a metal such asAl, Zn, Mg, Sn, Si, or the like. Alternatively, Ti, In, Cr, Ni, Cu, Pb,Fe, or the like may be used. These metal preferably has a purity of 99%or more, and more preferably 99.5% or more and is preferably processedinto grains, rods, tablets, wires, and crucibles.

[0279] Among the metals for metallization, an aluminum metallizationlayer is preferably formed on at least one side of the film from thepoint of view of durability of the metallization layer, productionefficiency, and cost. Other metal components such as nickel, copper,gold, silver, chromium, zinc, and the like may be metallizedsequentially or simultaneously with aluminum.

[0280] The metallization layer preferably has a thickness of 10 nm ormore, and more preferably 20 nm or more to achieve high gas barrierproperty. The upper limit of the thickness of the metallization layer isnot restricted; however, the thickness is preferably less than 50 nmfrom the point of view of economical and production efficiencies.

[0281] The gloss of the metallization layer is preferably 600% or more,and more preferably 700% or more.

[0282] Alternatively, a metallization layer composed of metal oxide maybe formed so that the film may be used as a transparent gas-barrier filmfor packaging having a superior gas barrier property. The metal oxidemetallization layer is preferably a layer of a metal oxide such asincompletely oxidized aluminum, or incompletely oxidized silicon.Incompletely oxidized aluminum is particularly preferable from the pointof view of durability of the metallization layer, production efficiency,and cost. Metallization can be performed by publicly known methods. Forexample, in depositing the metallization layer composed of incompletelyoxidized aluminum, the film is allowed to run in a high-vacuum devicehaving a degree of vacuum of 10-4 Torr or less, aluminum metal isheated, melted, and evaporated, and a small amount of oxygen gas issupplied at the site of evaporation so that the aluminum can becoherently deposited on the film surface to form a metallization layerwhile being oxidized. The thickness of the metal oxide metallizationlayer is preferably in the range of 10 to 50 nm, and more preferably 10to 30 nm. The oxidation of the metal oxide metallization layer composedof incompletely oxidized metal proceeds after metallization and changesthe light transmittance of the metal oxide metallization film. The lighttransmittance is preferably in the range of 70 to 90%. A lighttransmittance of less than 70% is not preferred since the content cannotbe seen through the package when the film is made into a packaging bag.A light transmittance exceeding 90% is not preferred because the gasbarrier property tends to be poor when the film is made into a packagingbag.

[0283] The adhesive strength between the metallization layer and thecoating layer of the metallized biaxially stretched polypropylene filmof the present invention and between the metal oxide metallization layerand the coating layer of the metallized biaxially stretchedpolypropylene film of the present invention is preferably 0.6 N/cm ormore, and more preferably 0.8 N/cm or more. When the adhesive strengthis less than the above-described range, the metallization layer may bepicked off when the metallized film is being wound into a roll and whenthe metallized film is being wound off for converting, resulting indegradation of the gas barrier property.

[0284] The gas barrier properties of the films prepared by depositing ametallization layer of a metal and a oxide metal on the biaxiallystretched polypropylene films of the present invention are preferably asfollows. The water vapor permeability is preferably 4 g/m²/d or less,and more preferably 1 g/m²/d or less, and the oxygen permeability ispreferably 200 ml/m²/d/MPa or less, and more preferably 100 ml/m²/d/MPafor use in food packaging bags.

[0285] The biaxially stretched polypropylene films of the first, second,third, fourth, and fifth embodiments of the present invention have anincreased stiffness in the longitudinal direction compared withconventional biaxially stretched polypropylene films without degradingimportant properties such as dimensional stability and moisture-proofproperty. As a result, the films exhibit superior handling convenienceand excellent tension resistance against converting tension appliedduring film converting such as printing, laminating, coating,metallizing, and bag-making. Moreover, the troubles such as cracks andprint pitch displacement due to the quality of base films can beavoided. Furthermore, the stiffness in the longitudinal direction andthe tension resistance are higher than those of the conventionalpolypropylenes having the same thickness; hence, the converting propertycan be maintained with a thickness smaller than that of conventionalbiaxially stretched polypropylene films. Accordingly, the biaxiallystretched polypropylene films of the present invention are suitable forpackaging and industrial use.

[0286] (Methods for Determined Characteristic Values)

[0287] The technical terms and the measurement methods employed in thepresent invention will now be described.

[0288] (1) Melt Strength (MS)

[0289] The melt strength MS was measured according to JapaneseIndustrial Standards (JIS) K7210. A polypropylene was heated to 230° C.in a melt-tension tester available from Toyo Seiki Kogyo Co., Ltd., andthe molten polypropylene was extruded at an extrusion speed of 15 mm/minto make a strand. The tension of the strand at a take-over rate of 6.5m/min was measured, and this tension was defined as the melt strength(MS).

[0290] (2) Melt Flow Rate (MFR)

[0291] The melt flow rate was measured according to the polypropylenetesting method of JIS K6758 at 230° C. and 2.16 kgf.

[0292] (3) Trouton Ratio

[0293] The Trouton ratio was measured by a converging flow methodaccording to a theory by Cogswell [Polymer Engineering Science, 12, 64(1972)] under the following conditions:

[0294] Apparatus: twin-capillary rheometer RH-2200 (available fromRosand Inc.)

[0295] Temperature: 230° C. Capillary size: Die/1.0 mm diam × 16 mmOrifice/1.0 mm diam × 0.25 mm Shear rate: approximately 10 s⁻¹ toapproximately 1800 s⁻¹ Extensional strain rate: approximately 2 s⁻¹ toapproximately 180 s⁻¹

[0296] Each sample was fed into the apparatus and maintained at 230° C.for 3 minutes. The sample was fed again and maintained for 3 minutes.Subsequently, the measurements were taken.

[0297] According to Cogswell's theory, the pressure drop of theconverging flow (ΔP_(ent)) at the entrance of the capillary can beexpressed in terms of extensional viscosity and shear viscosity as theexpression below:${\Delta \quad P_{ent}} = {\frac{4\sqrt{2}}{3\left( {n + 1} \right)}{\gamma_{a}\left( {\eta_{s}\eta_{E}} \right)}^{1/2}}$

[0298] wherein η_(E): extensional viscosity, η_(s): shear viscosity,γ_(a): shear rate, and n is a flow index in the power law (σ_(s)=kγhda^(n,) σ_(s): shear stress)

[0299] With the twin-capillary rheometer, two capillaries of differentlengths can be simultaneously used so that the shear viscosity andΔP_(ent) at a particular shear rate can be simultaneously measured. Theextensional viscosity η_(E) can then be calculated from the equationbelow:$\eta_{E} = {\frac{9\left( {n + 1} \right)^{2}}{32\quad \eta_{s}}\left\lbrack \frac{\Delta \quad P_{ent}}{\gamma_{a}} \right\rbrack}^{2}$$ɛ = \frac{4\quad \eta_{s}\gamma_{a}^{2}}{3\left( {n + 1} \right)\Delta \quad P_{ent}}$

[0300] wherein ε: extensional stress. The obtained extensionalviscosity/extensional strain rate curve and shear viscosity/shear ratecurve were respectively approximated as exponential functions. Using theexponential functions, η_(E(60)) and η_(s(60)) at a strain rate of 60S⁻¹ were calculated. Based on these, the Trouton ratio at a strain rateof 60 s⁻¹ (the ratio of η_(E) to η_(s) at the same strain rate) wascalculated:

Trouton ratio=η_(E(60))/η_(s(60))

[0301] (4) Meso Pentad Fraction (mmmm)

[0302] A polypropylene was dissolved in o-dichlorobenzene-D6, and¹³C-NMR was measured at a resonance frequency of 67.93 MHz usingJNM-GX270 apparatus available from JEOL Ltd. The assignment of theobtained spectrum and the calculation of the meso pentad fraction wereperformed based on the method by T. Hayashi et. al (Polymer, 29, 138-143(1988)), in which, for a methyl-group-derived spectrum, each peaks wererespectively assigned with an mmmm peak of 21.855 ppm, the peak area wascalculated, and the ratio of the peak area to the total peak area of themethyl-group-derived peaks were calculated in terms of percentage. Thedetailed measurement conditions were as follows: Measurement density: 15to 20 wt. % Measurement solvent: o-dichlorobenzene (90 wt. %)/benzene-D6(10 wt. %) Measurement temperature: 120 to 130° C. Resonance frequency:67.93 MHz Pulse width: 10 microseconds (45° pulse) Pulse repeating time:7.091 seconds Data points: 32K Number of accumulation: 8168 Measurementmode: Noise decoupling

[0303] (5) Young's Modulus, F2 Value, and F5 Value

[0304] The Young's modulus, F2 value, and F5 value at 25° C. weremeasured at 65% RH using a film strength and elongation tester(AMF/RTA-100) available from Orientech Co., Ltd. A sample 15 cm in ameasuring direction and 1 cm in a direction perpendicular to themeasuring direction was prepared by cutting and was elongated at anoriginal length of 50 mm and a stretching rate of 300 mm/min. TheYoung's modulus was measured according to JIS-Z1702. The F2 value andthe F5 value were, respectively the stress applied on the sample at anelongation of 2% and at an elongation of 5%. When the measurementinvolves a high temperature, such as 80° C., a hot/cold thermostatavailable from Gondot Science, Ltd., under the same conditions describedabove.

[0305] (6) Observation of the Fibril Structure

[0306] A sample was placed in such a manner that the longitudinaldirection of the sample matches with the vertical direction of an image,and was then observed with an atomic force microscope (AFM) under thecondition described below. During observation, conditions such as gainand amplitude, etc. were suitably adjusted so that the image was notblurred. When blurring of the image was not corrected by adjusting theconditions, a cantilever was replaced. The sample was observed fivetimes each time at a different position for a field view of 1 μm (or 5μm, or 10 μm) square. A sample was evaluated as “A” when longitudinalfibrils having a width of 40 nm or more and extending across two sidesparallel to the transverse direction of the images were found in all ofthe five 10-μm square images. A sample was evaluated as “B” when suchlongitudinal fibrils were found in all of the five 5-μm square images,and a sample was evaluated as “C” when such longitudinal fibrils werefound in all of the five 1-μm images. A sample was evaluated as “NONE”when no longitudinal fibrils having a width of 40 nm or more wereobserved. The number and the width of the longitudinal fibrils of thesample were calculated and averaged from the number and the width of thelongitudinal fibrils having a width of 40 nm or more in each images.Note that it is preferable to observe both surfaces of the film;however, it is sufficient to observe only one surface of the film.Apparatus: NanoScope III AFM (manufactured by Digital Instruments, Co.)Cantilever: Single crystal of silicon Scan mode: Tapping mode Scanrange: 1 μm × 1 μm, 5 μm × 5 μm, 10 μm × 10 μm Scan rate: 0.3 Hz

[0307] (7) Isotactic Index (II)

[0308] A polypropylene was extracted with 60° C. or lower n-heptane for2 hours so as to remove the additives in the polypropylene, and wassubsequently vacuum-dried at 130° C. for 2 hours. A sample of weight W(mg) was taken therefrom, and extracted with boiled n-heptane in aSoxhlet extractor for 12 hours. The sample was then taken out,sufficiently washed with acetone, and vacuum-dried at 130° C. for 6hours. The sample was then cooled to normal temperature, and the weightW′ (mg) was measured. The isotactic index was then determined with thefollowing equation:

II=(W′/W)×100 (%)

[0309] (8) Intrinsic Viscosity ([η])

[0310] A polypropylene was dissolved in tetralin at 135° C., and theintrinsic viscosity was measured with an Ostwald viscometer manufacturedby Mitsui Toatsu Chemicals, Inc.

[0311] (9) Glass Transition Temperature (Tg)

[0312] Into a thermal analysis apparatus RDC 220 available from SeikoInstruments, Inc., 5 mg of a sample enclosed in an aluminum pan was fed,and the temperature was increased at a rate of 20 ° C./min. Using theinternal program of a thermal analysis system SSC5200 available fromSeiko Instruments, Inc., the starting point of glass transition wasdetermined from the resulting thermal curve and this temperature wasdefined as the glass transition temperature (Tg).

[0313] (10) Bromine Number

[0314] The bromine number was measured according to JIS K2543-1979. Thenumber of grams of bromine added to the unsaturated components in a100-g of sample oil was defined as the bromine number.

[0315] (11) Heat Shrinkage

[0316] The measurement was performed in the longitudinal direction andin the transverse direction. A film sample having a length of 260 mm anda width of 10 mm was prepared, and a mark was placed at a positioncorresponding to a length of 200 mm, i.e., the original length L₀. Thesample was heated at 120° C. for 15 minutes in a heat flow convectionoven while being applied with a load of 3 g at the lower end of thesample. The sample was then discharged into room temperature, and themarked length (L₁) of the sample was measured. The heat shrinkage wascalculated by the equation below. This process was performed for eachdirection (longitudinal direction and transverse direction), and the sumof the heat shrinkages in the longitudinal direction and the transversedirection was calculated.

Heat shrinkage (%)=100×(L ₀ −L ₁)/L ₀

[0317] (12) Centerline Average Roughness (Ra)

[0318] The centerline average roughness (Ra) was measured according toJIS B0601 using stylus-type roughness meter. A high-accuracy thin-filmstep-difference measuring instrument (type:ET-30HK), manufactured byKosaka Laboratory Ltd., was used. The conical stylus had a radius of 0.5μm, the load was 16 mg, and the cut-off was 0.08 mm.

[0319] The portion of the roughness curve corresponding to themeasurement length L was cut off in the center line direction, and thecenterline average roughness (Ra) in terms of μm was calculated by theequation below, wherein the centerline of the portion cut off is the Xaxis, the longitudinal direction of the portion cut off is the Y axis,and the roughness curve is represented by y=f(x):${R\quad a} = {\frac{1}{L}{\int{{{f(x)}}{x}}}}$

[0320] (13) Thickness of the Coating Layer, Metallization Layer, andMetal Oxide Metallization Layer

[0321] Using a transmission electron microscope (TEM), the structure ofa film cross-section was observed, and the thickness of the depositedlayer and the thickness constructions were measured.

[0322] (14) Surface Gloss of the Film

[0323] The surface gloss of the film as a 60° specular gloss wasmeasured with a digital variable angle gloss meter UGV-5D manufacturedby Suga Test Instruments Co., Ltd. according to JIS Z8741 method.

[0324] (15) Surface Gloss of the Metallized Film

[0325] A metallized biaxially stretched polypropylene film was installedin a continuous vacuum metallizing apparatus. While allowing aluminum toevaporate from an electron-beam heating type evaporation source andallowing the film to run continuously, aluminum was deposited so thatthe optical density (−log(optical transmittance)) measured using a anoptical densitometer (TR927) manufactured by Macbeth was in the range of1.9 to 2.1. The surface gloss of the metallized film was measuredaccording to JIS Z8741.

[0326] (16) Adhesive Strength

[0327] The adhesive strength between the surface layer of the biaxiallystretched polypropylene film and the coating layer after metallizationwas measured as below. A biaxially oriented polypropylene film having athickness of 20 μm (S645, manufactured by Toray Industries, Inc.) waslaminated on the side of the coating layer using a polyurethane-basedadhesive, and was left to stand at 40° C. for 48 hours. A 90° peel at apeeling rate of 10 cm/min was performed at a width of 15 mm usingTensilon manufactured by Toyo Baldwin Co. Ltd. The adhesive strengthsbetween the polypropylene film for metallization and the metallizationlayer and that between the polypropylene film for metallization and themetal oxide metallization layer are measured by the same methoddescribed above in which a biaxially oriented polypropylene film havinga thickness of 20 μm (S645, manufactured by Toray Industries, Inc.) waslaminated on the side of the metallization layer and on the side of themetal oxide metallization layer using a polyurethane-based adhesive.

[0328] (17) Oxygen Permeability

[0329] A polypropylene adhesive film (Scotchmark, manufactured by 3MCompany, 40 μm in thickness) was attached on the metallized side of abiaxially stretched polypropylene film, and the oxygen permeability wasmeasured at 23° C. and a relative humidity of 0% using an oxygenpermeability measuring instrument Oxtran 2/20 manufactured byMOCON/Modern Controls Inc.

[0330] (18) Water Vapor Permeability

[0331] The water vapor permeability of a biaxially stretchedpolypropylene film was measured at 40° C. and a relative humidity of 90%using a water vapor permeability measuring instrument PERMATRAN-W3/30manufactured by MOCON/Modern Controls Inc. The water vapor permeabilityof a metallized biaxially stretched polypropylene film was measured asdescribed above but with a polypropylene adhesive film (Scotchmark,manufactured by 3M Company, 40 μm in thickness) attached on themetallized side.

[0332] (19) Real Stretching Ratio

[0333] An unstretched film was prepared by extruding a material from aslit die and winding the extruded material on a metal drum so as to becooled and solidified into a sheet. A 1-cm square mark the sides ofwhich extend in the longitudinal and transverse direction of the filmwas inscribed on the unstretched film, and the unstretched film wasstretched and wound. Subsequently, the length (cm) of the inscribedsquare mark on the film was measured, and the real stretching ratios inthe longitudinal direction and the transverse direction were determined.

[0334] (20) Converting Ability

[0335] An unstretched polypropylene film having a thickness of 20 μm waslaminated on a biaxially stretched polypropylene film or a metallizedbiaxially stretched polypropylene film (on the opposite side of themetallization layer) of the present invention having a length of 1,000 mand a thickness of 15 μm so as to prepare a food-packaging film. Withthe unstretched polypropylene film facing inward, the film was installedin a cylindrical manner using a vertical-type pillow-packaging machine(Fuji FW-77) manufactured by Fuji Machinery Co., Ltd., and was formedinto bags.

[0336] In bag-making, a film that did not have wrinkles or elongatedportions and that was processed into bags with good appearance wasevaluated as “good”. A film that was processed into bags with poorappearance since the bag had elongated portions due to a low Young'smodulus of the film in the longitudinal direction and low firmness, orsince the bag had wrinkles due to a poor slipperiness and a large heatshrinkage, was evaluated as “poor”.

EXAMPLES

[0337] The present invention will now be described based on Examples.Unless otherwise noted, the screw speed of the extruder and the rotatingspeed of the cooling drum were adjusted to predetermined values toobtain a film having a desired thickness.

Example 1

[0338] To 90 percent by weight of a polypropylene prepared by blending apublicly known polypropylene having a melt strength (MS) of 1.5 cN, amelt flow rate (MFR) of 2.3 g/10 min, a meso pentad fraction (mmmm) of92%, and an isotactic index (II) of 96% with 10 percent by weight of ahigh-melt-strength polypropylene (HMS-PP) having a melt strength of 20cN, a melt flow rate (MFR) of 3 g/10 min, a meso pentad fraction (mmmm)of 97%, and an isotactic index (II) of 96.5%, containing long-chainbranches, and satisfying the above-described formula (1) between themelt strength (MS) and the melt flow rate (MFR), 10 percent by weight ofpolydicyclopentadiene having Tg of 80° C., a bromine number of 3 cg/g,and a hydrogenation rate of 99%, which is a petroleum resinsubstantially containing no polar-group, was added as an additive thathas compatibility with the polypropylene and can provide plasticityduring stretching to prepare a resin. To 100 parts by weight of thisresin, 0.15 parts by weight of crosslinked particles of apolymethacrylicacid-based polymer (crosslinked PMMA) having an averageparticle size of 2 μm was added as crosslinked organic particles, and0.8 parts by weight of a 1:1 mixture of glycerin fatty acid ester andalkyldiethanolamine fatty acid ester was added as an antistatic agent.The resulting mixture was fed into a twin-screw extruder, was extrudedat 240° C. into a gut-shape, cooled in a 20° C. water bath, and cut intoa 3-mm length by a chip cutter. The resulting chips were dried for 2hours at 100° C., fed into a single-screw extruder, melted at 260° C.,and filtered. The resulting filtered material was extruded from a slitdie and formed into a sheet by winding on a metal drum having atemperature of 25° C.

[0339] This sheet was passed between rolls maintained at 135° C., andpre-heated, and passed between rolls, which had different rotating speedand were maintained at 140° C., so that the sheet is stretched to 8times the initial length in the longitudinal direction. The stretchedsheet was then immediately cooled to room temperature. The stretchedfilm was next fed into a tenter to be pre-heated at 165° C., stretchedin the transverse direction to 7 times the initial length at 160° C.,and heat-set at 160° C. while being relaxed in the transverse directionby 6%. The film was then cooled and wound so as to obtain a biaxiallystretched polypropylene film having a thickness of 15 μm.

[0340] The composition of the raw material and the results of theevaluation of the film characteristics are shown in Tables 1 and 2. Theresulting film had a high Young's modulus in the longitudinal directionand superior tension resistance, dimensional stability, moisture-proofproperty, and converting ability.

Example 2

[0341] A biaxially stretched polypropylene film of EXAMPLE 2 having athickness of 15 μm was prepared as in EXAMPLE 1 except that a stretchingratio in the longitudinal direction was increased to 10.

[0342] The results are shown in Tables 1 and 2. The resulting film had ahigh Young's modulus in the longitudinal direction and superior tensionresistance, dimensional stability, moisture-proof property, andconverting ability.

Example 3

[0343] A biaxially stretched polypropylene film of EXAMPLE 3 having athickness of 15 μm was prepared as in EXAMPLE 1 except that 5 percent byweight of the HMS-PP having long-chain branches was blended and 3percent by weight of polydicyclopentadiene was added. Moreover, the filmwas stretched to 8 times the initial length in the longitudinaldirection and to 8 times the initial length in the transverse direction.

[0344] The results are shown in Tables 1 and 2. The resulting film had ahigh Young's modulus in the longitudinal direction and superior tensionresistance, dimensional stability, moisture-proof property, andconverting ability.

Example 4

[0345] A biaxially stretched polypropylene film of EXAMPLE 4 having athickness of 15 μm was prepared as in EXAMPLE 3 except that 3 percent byweight of the HMS-PP having long-chain branches was blended.

[0346] The results are shown in Tables 1 and 2. The resulting film had ahigh Young's modulus in the longitudinal direction and superior tensionresistance, dimensional stability, moisture-proof property, andconverting ability.

Example 5

[0347] A biaxially stretched polypropylene film of EXAMPLE 5 having athickness of 15 μm was prepared as in EXAMPLE 1 except that 5 percent byweight of β-pinene having a Tg of 75° C., a bromine number of 4 cg/g,and a hydrogenation rate of 99%, which is a terpene resin substantiallycontaining no polar-group, was added as an additive that has acompatibility with the polypropylene and can provide plasticity duringstretching, and that the film is stretched to 9 times the initial lengthin the longitudinal direction and to 7 times the initial length in thetransverse direction.

[0348] The results are shown in Tables 1 and 2. The resulting film had ahigh Young's modulus in the longitudinal direction and superior tensionresistance, dimensional stability, moisture-proof property, andconverting ability.

Example 6

[0349] To 100 parts by weight of a resin composition containing 85percent by weight of a HMS-PP containing long-chain branches and havinga melt strength (MS) of 20 cN, a melt flow rate (MFR) of 3 g/10 min, ameso pentad fraction (mmmm) of 97%, and an isotactic index (II) of96.5%, and satisfying the formula below between the melt strength (MS)and the melt flow rate (MFR)

log(MS)>−0.61 log(MFR)+0.82

[0350] and 15 percent by weight of hydrogenated β-dipentene having a Tgof 75° C., a bromine number of 3 cg/g, and a hydrogenation rate of 99%,which was a terpene resin substantially containing no polar-group, as anadditive that has a compatibility with the polypropylene and can provideplasticity during stretching, 0.15 parts by weight of crosslinkedparticles of polystyrene-based polymer (crosslinked PS) having anaverage particle size of 1 μm was added as crosslinked organicparticles. Furthermore, 0.8 parts by weight of a 1:1 mixture of glycerinfatty acid ester and alkyldiethanolamine fatty acid ester was added asan antistatic agent. The resulting mixture was fed into a twin-screwextruder, was extruded at 240° C. into a gut-shape, cooled in a 20° C.water bath, and cut into a 3-mm length by a chip cutter. The resultingchips were dried for 2 hours at 100° C., fed into a single-screwextruder, melted at 260° C., and filtered. The resulting filteredmaterial was extruded from a slit die and formed into a sheet by windingon a metal drum having a temperature of 30° C.

[0351] This sheet was passed between rolls maintained at 133° C., andpre-heated, and passed between rolls, which had different rotating speedand were maintained at 138° C., so that the sheet is stretched to 8times the initial length in the longitudinal direction. The stretchedsheet was then immediately cooled to room temperature. The stretchedfilm was next fed into a tenter to be pre-heated at 163° C., stretchedin the transverse direction to 8 times the initial length at 160° C.,and heat-set at 160° C. while being relaxed in the transverse directionby 8%. The film was then cooled and wound so as to obtain a biaxiallystretched polypropylene film having a thickness of 15 μm.

[0352] The results are shown in Tables 1 and 2. The resulting film had ahigh Young's modulus in the longitudinal direction and superior tensionresistance, dimensional stability, moisture-proof property, andconverting ability.

Example 7

[0353] A biaxially stretched polypropylene film having a thickness of 15μm was prepared as in EXAMPLE 6 except that to 80 percent by weight of apolypropylene prepared by blending a publicly known polypropylene havinga melt strength (MS) of 1.5 cN, a melt flow rate (MFR) of 2.3 g/10 min,a meso pentad fraction (mmmm) of 92%, and an isotactic index (II) of 96%with 5 percent by weight of a HMS-PP having a melt strength (MS) of 20cN, a melt flow rate (MFR) of 3 g/10 min, a meso pentad fraction (mmmm)of 97%, and an isotactic index (II) of 96.5%, containing long-chainbranches, and satisfying the above-described formula (1) between themelt strength (MS) and the melt flow rate (MFR), 20 percent by weight ofa mixture containing β-pinene having a Tg of 75° C., a bromine number of4 cg/g, and a hydrogenation rate of 99% and hydrogenated β-dipenteneresin having a Tg of 75° C., a bromine number of 3 cg/g, and ahydrogenation rate of 99%, which are terpene resins substantiallycontaining no polar-group, as additives that has a compatibility withthe polypropylene and can provide plasticity during stretching.Moreover, the film was stretched to 11 times the initial length in thelongitudinal direction, and to 6 times the initial length in thetransverse direction.

[0354] The results are shown in Tables 1 and 2. The resulting film had ahigh Young's modulus in the longitudinal direction and superior tensionresistance, dimensional stability, moisture-proof property, andconverting ability.

Example 8

[0355] A biaxially stretched polypropylene film of EXAMPLE 8 having athickness of 15 μm was prepared as in EXAMPLE 3, except that a HMS-PPthat contains long-chain branches and has a melt strength (MS) of 15 cN,a melt flow rate (MFR) of 2.0 g/10 min, a meso pentad fraction (mmmm) of96.5%, and an isotactic index (II) of 97%, satisfies the above-describedformula (1) between the melt strength (MS) and the melt flow rate (MFR),was used as the HMS-PP.

[0356] The results are shown in Tables 1 and 2. The resulting film had ahigh Young's modulus in the longitudinal direction and superior tensionresistance, dimensional stability, moisture-proof property, andconverting ability.

Example 9

[0357] A biaxially stretched polypropylene film of EXAMPLE 9 having athickness of 15 μm was prepared as in EXAMPLE 3, except that a HMS-PPcontaining long-chain branches, and having a melt strength (MS) of 30cN, a melt flow rate (MFR) of 2.1 g/10 min, a meso pentad fraction(mmmm) of 97%, and an isotactic index (II) of 97%, and satisfying theformula below between the melt strength (MS) and the melt flow rate(MFR) was used as the HMS-PP:

log(MS)>−0.61 log(MFR)+0.82

[0358] The results are shown in Tables 1 and 2. The resulting film had ahigh Young's modulus in the longitudinal direction and superior tensionresistance, dimensional stability, moisture-proof property, andconverting ability.

Example 10

[0359] A biaxially stretched polypropylene film of EXAMPLE 10 having athickness of 15 μm was prepared as in EXAMPLE 5, except that 20 percentby weight of HMS-PP containing long-chain branches was blended, and thatpolydicyclopentadiene having Tg of 80° C., a bromine number of 3 cg/g,and a hydrogenation rate of 99%, which is a petroleum resinsubstantially containing no polar-group, as an additive that hascompatibility with the polypropylene and can provide plasticity duringstretching, was added.

[0360] The results are shown in Tables 1 and 2. The resulting film had ahigh Young's modulus in the longitudinal direction and superior tensionresistance, dimensional stability, moisture-proof property, andconverting ability.

Example 11

[0361] A biaxially stretched polypropylene film of EXAMPLE 11 having athickness of 15 μm was prepared as in EXAMPLE 10 except that 30 percentby weight of HMS-PP was blended.

[0362] The results are shown in Tables 1 and 2. The resulting film had ahigh Young's modulus in the longitudinal direction and superior tensionresistance, dimensional stability, moisture-proof property, andconverting ability.

Example 12

[0363] A biaxially stretched polypropylene film of EXAMPLE 12 having athickness of 15 μm was prepared as in EXAMPLE 10 except that 50 percentby weight of HMS-PP was added.

[0364] The results are shown in Tables 1 and 2. The resulting film had ahigh Young's modulus in the longitudinal direction and superior tensionresistance, dimensional stability, moisture-proof property, andconverting ability.

EXAMPLE 13

[0365] A biaxially stretched polypropylene film of EXAMPLE 13 having athickness of 15 μm was prepared as in EXAMPLE 1 except that an HMS-PPcontaining long-chain branches and having a melt strength (MS) of 1 cN,a melt flow rate (MFR) of 10 g/10 min, a meso pentad fraction (mmmm) of98%, and an isotactic index (II) of 98.5%, was blended.

[0366] The results are shown in Tables 1 and 2. The resulting film had ahigh Young's modulus in the longitudinal direction and superior tensionresistance, dimensional stability, moisture-proof property, andconverting ability.

Example 14

[0367] A biaxially stretched polypropylene film of EXAMPLE 14 having athickness of 15 μm was prepared as in EXAMPLE 1 except that apolypropylene prepared by blending a publicly known polypropylene havinga melt strength (MS) of 1.1 cN, a melt flow rate (MFR) of 3 g/10 min, ameso pentad fraction (mmmm) of 97.5%, and an isotactic index (II) of 99%with 10 percent by weight of the HMS-PP was used. Moreover, the film wasstretched to 9 times the initial length in the longitudinal directionand 9 times the initial length in the transverse direction.

[0368] The results are shown in Tables 1 and 2. The resulting film had ahigh Young's modulus in the longitudinal direction and superior tensionresistance, dimensional stability, moisture-proof property, andconverting ability.

Example 15

[0369] A biaxially stretched polypropylene film of EXAMPLE 15 having athickness of 15 μm was prepared as in EXAMPLE 3 except that apolypropylene prepared by blending a publicly known polypropylene havinga melt strength (MS) of 1.2 cN, a melt flow rate (MFR) of 2.7 g/10 min,a meso pentad fraction (mmmm) of 96%, and an isotactic index (II) of 98%with 5 percent by weight of the HMS-PP was used.

[0370] The results are shown in Tables 1 and 2. The resulting film had ahigh Young's modulus in the longitudinal direction and superior tensionresistance, dimensional stability, moisture-proof property, andconverting ability. TABLE 1 Characteristics of polypropylene resinCharacteristics of HMS-PP resin MS MFR −0.61log(MFR) + formula (1)Content (cN) (g/10 min) log(MS) 0.82 satisfied? (wt. %) EXAMPLE 1 20.03.0 1.30 0.53 Yes 10 EXAMPLE 2 20.0 3.0 1.30 0.53 Yes 10 EXAMPLE 3 20.03.0 1.30 0.53 Yes 5 EXAMPLE 4 20.0 3.0 1.30 0.53 Yes 3 EXAMPLE 5 20.03.0 1.30 0.53 Yes 10 EXAMPLE 6 20.0 3.0 1.30 0.53 Yes 100 EXAMPLE 7 20.03.0 1.30 0.53 Yes 5 EXAMPLE 8 15.0 2.0 1.18 0.64 Yes 5 EXAMPLE 9 30.02.1 1.48 0.62 Yes 5 EXAMPLE 10 20.0 3.0 1.30 0.53 Yes 20 EXAMPLE 11 20.03.0 1.30 0.53 Yes 30 EXAMPLE 12 20.0 3.0 1.30 0.53 Yes 50 EXAMPLE 13 1.010.0 0.00 0.21 No 10 EXAMPLE 14 20.0 3.0 1.30 0.53 Yes 10 EXAMPLE 1520.0 3.0 1.30 0.53 Yes 5 Characteristics of polypropylene resin MesoPentad MS MFR −0.61log(MFR) + formula (2) Fraction (cN) (g/10 min)log(MS) 0.52 satisfied? (%) EXAMPLE 1 3.0 2.3 0.48 0.30 Yes 92.5 EXAMPLE2 3.0 2.3 0.48 0.30 Yes 92.5 EXAMPLE 3 2.7 2.2 0.43 0.31 Yes 92.3EXAMPLE 4 2.4 2.3 0.38 0.30 Yes 92.2 EXAMPLE 5 3.0 2.3 0.48 0.30 Yes92.5 EXAMPLE 6 20.0 3.0 1.30 0.23 Yes 97.0 EXAMPLE 7 2.7 2.2 0.43 0.31Yes 92.5 EXAMPLE 8 2.6 2.2 0.41 0.31 Yes 92.2 EXAMPLE 9 3.4 2.2 0.530.31 Yes 92.3 EXAMPLE 10 3.3 2.4 0.52 0.29 Yes 93.0 EXAMPLE 11 3.6 2.40.56 0.29 Yes 93.5 EXAMPLE 12 3.5 2.5 0.54 0.28 Yes 94.5 EXAMPLE 13 2.03.0 0.30 0.23 Yes 92.6 EXAMPLE 14 2.7 3.0 0.43 0.23 Yes 97.5 EXAMPLE 152.8 2.7 0.45 0.26 Yes 96.1 Content Petroleum resin and ContentStretching ratio (wt. %) terpene resin (wt. %) (longitudinal ×transverse) EXAMPLE 1 90 hydrogenated 10 8 × 7 dicyclopentadiene EXAMPLE2 90 hydrogenated 10 10 × 6  dicyclopentadiene EXAMPLE 3 97 hydrogenated3 8 × 8 dicyclopentadiene EXAMPLE 4 97 hydrogenated 3 8 × 8dicyclopentadiene EXAMPLE 5 95 hydrogenated β- 5 9 × 7 pinene EXAMPLE 685 hydrogenated β- 15 8 × 8 dipentene EXAMPLE 7 80 hydrogenated β- 20 11× 6  pinene and hydrogenated β- dipentene EXAMPLE 8 97 hydrogenated 3 8× 8 dicyclopentadiene EXAMPLE 9 97 hydrogenated 3 8 × 8dicyclopentadiene EXAMPLE 10 95 hydrogenated 5 9 × 7 dicyclopentadieneEXAMPLE 11 95 hydrogenated 5 9 × 7 dicyclopentadiene EXAMPLE 12 95hydrogenated 5 9 × 7 dicyclopentadiene EXAMPLE 13 90 hydrogenated 10 8 ×7 dicyclopentadiene EXAMPLE 14 90 hydrogenated 10 9 × 9dicyclopentadiene EXAMPLE 15 97 hydrogenated 3 8 × 8 dicyclopentadiene

[0371] TABLE 2 Young's Young's modulus modulus F2 value F5 value(longitudinal) (transverse) m value at (longitudinal) (longitudinal) at25° C. at 25° C. 25° C. at 25° C. at 25° C. (GPa) (GPa) (−) (MPa) (Mpa)EXAMPLE 1 3.7 4.2 0.47 60 82 EXAMPLE 2 4.3 3.5 0.55 72 103 EXAMPLE 3 3.13.5 0.47 48 64 EXAMPLE 4 2.7 3.8 0.42 43 55 EXAMPLE 5 3.6 3.7 0.49 58 87EXAMPLE 6 4.0 3.7 0.52 61 92 EXAMPLE 7 5.2 4.7 0.53 80 115 EXAMPLE 8 2.93.8 0.43 45 58 EXAMPLE 9 3.5 3.3 0.51 58 74 EXAMPLE 10 3.4 3.5 0.49 5163 EXAMPLE 11 3.3 3.6 0.48 50 63 EXAMPLE 12 3.1 3.1 0.50 47 60 EXAMPLE13 2.6 3.7 0.41 41 53 EXAMPLE 14 3.6 4.2 0.46 63 79 EXAMPLE 15 3.3 4.00.45 53 65 Young's modulus Young's modulus (longitudinal) (transverse)at at 80° C. (GPa) 80° C. (GPa) m value at 80° C. (−) EXAMPLE 1 0.590.65 0.48 EXAMPLE 2 0.65 0.58 0.53 EXAMPLE 3 0.50 0.48 0.51 EXAMPLE 40.45 0.50 0.47 EXAMPLE 5 0.58 0.55 0.51 EXAMPLE 6 0.67 0.70 0.49 EXAMPLE7 0.80 0.75 0.52 EXAMPLE 8 0.47 0.58 0.45 EXAMPLE 9 0.53 0.48 0.52EXAMPLE 10 0.56 0.50 0.53 EXAMPLE 11 0.57 0.52 0.52 EXAMPLE 12 0.60 0.530.53 EXAMPLE 13 0.42 0.48 0.47 EXAMPLE 14 0.78 0.65 0.55 EXAMPLE 15 0.690.68 0.50 Heat Heat shrinkage shrinkage Sum of heat Water vapor(longitudinal) (transverse) at shrinkage at permeability at 120° C. 120°C. 120° C. (g/m²/d/0.1 Converting (%) (%) (%) mm) ability EXAMPLE 1 3.30.6 3.9 0.8 Good EXAMPLE 2 4.0 1.0 5.0 0.7 Good EXAMPLE 3 3.0 0.5 3.51.2 Good EXAMPLE 4 3.1 0.6 3.7 1.3 Good EXAMPLE 5 3.0 0.7 3.7 1.0 GoodEXAMPLE 6 2.9 0.7 3.6 0.8 Good EXAMPLE 7 4.2 1.5 5.7 0.5 Good EXAMPLE 82.5 0.6 3.1 1.2 Good EXAMPLE 9 3.1 0.5 3.6 1.1 Good EXAMPLE 10 3.0 0.53.5 1.0 Good EXAMPLE 11 2.9 0.5 3.4 1.0 Good EXAMPLE 12 2.9 0.4 3.3 0.9Good EXAMPLE 13 3.0 1.0 4.0 0.8 Good EXAMPLE 14 1.6 0.3 1.9 0.5 GoodEXAMPLE 15 1.5 0.2 1.7 1.2 Good

Comparative Example 1

[0372] To 100 parts by weight of a publicly known polypropylene having amelt strength (MS) of 1.5 cN, a melt flow rate (MFR) of 2.3 g/10 min, ameso pentad fraction (mmmm) of 92%, and an isotactic index (II) of 96%,not satisfying the above-described formula (2) between the melt strength(MS) and the melt flow rate (MFR), 0.15 parts by weight of crosslinkedparticles of a polymethacrylicacid-based polymer (crosslinked PMMA)having an average particle size of 2 μm was added as crosslinked organicparticles, and 0.8 parts by weight of a 1:1 mixture of glycerin fattyacid ester and alkyldiethanolamine fatty acid ester was added as anantistatic agent. The mixture was fed into a singlescrew extruder,melted at 260° C., filtered, extruded from a slit die, and formed into asheet by winding around a 25° C. metal drum.

[0373] This sheet was passed between rolls maintained at 130° C., andpre-heated, and passed between rolls, which had different rotating speedand were maintained at 135° C., so that the sheet is stretched to 5times the initial length in the longitudinal direction. The stretchedsheet was then immediately cooled to room temperature. The stretchedfilm was next fed into a tenter to be pre-heated at 165° C., stretchedin the transverse direction to 10 times the initial length at 160° C.,and heat-set at 160° C. while being relaxed in the transverse directionby 7%. The film was then cooled and wound so as to obtain a biaxiallystretched polypropylene film having a thickness of 15 μm.

[0374] The results are shown in Tables 3 and 4. The resulting film had alow Young's modulus in the longitudinal direction, poor tensionresistance, moisture-proof property, and converting ability.

Comparative Example 2

[0375] A biaxially stretched polypropylene film of COMPARATIVE EXAMPLE 2having a thickness of 15 μm was prepared as in COMPARATIVE EXAMPLE 1except that the stretching ratio in the longitudinal direction wasincreased to 7.

[0376] The results are shown in Tables 3 and 4. Because a significantdegree of film breakage occurred during transverse stretching, thesufficient film couldn't be obtained.

Comparative Example 3

[0377] A biaxially stretched polypropylene film of COMPARATIVE EXAMPLE 3having a thickness of 15 μm was prepared as in COMPARATIVE EXAMPLE 1except that a publicly known polypropylene having a melt strength (MS)of 1.1 cN, a melt flow rate (MFR) of 3 g/10 min, a meso pentad fraction(mmmm) of 97.5%, and an isotactic index (II) of 99% was used.

[0378] The results are shown in Tables 3 and 4. Because the edges of thefilm rode up when the film in the molten state was wound on a coolingdrum, the sheet frequently broke during longitudinal stretching.Moreover, film breakage occurred during transverse stretching, overallfilm formability was poor, and the film was not suited for industrialproduction.

Comparative Example 4

[0379] A biaxially stretched polypropylene film of COMPARATIVE EXAMPLE 4having a thickness of 15 μm was prepared as in COMPARATIVE EXAMPLE 1except that a publicly known polypropylene having a melt strength (MS)of 0.6 cN, a melt flow rate (MFR) of 6 g/10 min, a meso pentad fraction(mmmm) of 99.8%, and an isotactic index (II) of 99.5% was used.

[0380] The results are shown in Tables 3 and 4. Because a significantdegree of film breakage occurred during transverse stretching, thesufficient film couldn't be obtained.

Comparative Example 5

[0381] A biaxially stretched polypropylene film of COMPARATIVE EXAMPLE 5having a thickness of 15 μm was prepared as in COMPARATIVE EXAMPLE 1except that 3 percent by weight of polydicyclopentadiene having Tg of80° C., a bromine number of 3 cg/g, and a hydrogenation rate of 99%,which is a petroleum resin substantially containing no polar-group as anadditive that has compatibility with the polypropylene and can provideplasticity during stretching. Moreover, the film was stretched to 5times the initial length in the longitudinal direction and 9 times theinitial length in the transverse direction.

[0382] The results are shown in Tables 3 and 4. The resulting film had alow Young's modulus in the longitudinal direction, poor tensionresistance and converting ability.

Comparative Example 6

[0383] A biaxially stretched polypropylene film of COMPARATIVE EXAMPLE 6having a thickness of 15 μm was prepared as in COMPARATIVE EXAMPLE 5except that the film was stretched to 7 times the initial length in thelongitudinal direction and 8 times the initial length in the transversedirection.

[0384] The results are shown in Tables 3 and 4. Because film breakageoccurred during transversal stretching, a film having a sufficientlength could not be obtained, and the film was not suited for industrialproduction.

Comparative Example 7

[0385] A biaxially stretched polypropylene film of COMPARATIVE EXAMPLE 7having a thickness of 15 μm was prepared as in COMPARATIVE EXAMPLE 5except that the stretching ratio in the longitudinal direction wasincreased to 8.

[0386] The results are shown in Tables 3 and 4. Because a significantlydegree of film breakage occurred during transverse stretching, thesufficient film could not be obtained.

Comparative Example 8

[0387] A biaxially stretched polypropylene film of COMPARATIVE EXAMPLE 8having a thickness of 15 μm was prepared as in COMPARATIVE EXAMPLE 5except that 10 percent by weight of polydicyclopentadiene was added.

[0388] The results are shown in Tables 3 and 4. The resulting film had alow Young's modulus in the longitudinal direction at 80° C., poortension resistance, dimensional stability, and converting ability.

Comparative Example 9

[0389] A biaxially stretched polypropylene film of COMPARATIVE EXAMPLE 9having a thickness of 15 μm was prepared as in COMPARATIVE EXAMPLE 8except that the film was stretched to 8 times the initial length in thelongitudinal direction and 7 times the initial length in the transversedirection.

[0390] The results are shown in Tables 3 and 4. Because film breakageoccurred during transverse stretching, a film having a sufficient lengthcould not be obtained, and the film was not suited for industrialproduction.

Comparative Example 10

[0391] A biaxially stretched polypropylene film of COMPARATIVE EXAMPLE10 having a thickness of 15 μm was prepared as in COMPARATIVE EXAMPLE 8except that the stretching ratio in the longitudinal direction wasincreased to 9.

[0392] The results are shown in Tables 3 and 4. Because a significantdegree of film breakage occurred during transverse stretching,sufficient film could not be obtained.

Comparative Example 11

[0393] A biaxially stretched polypropylene film of COMPARATIVE EXAMPLE11 having a thickness of 15 μm was prepared as in EXAMPLE 6 except thatonly the HMS-PP containing long-chain branches, satisfying theabove-described formula (1) between the melt strength (MS) and the meltflow rate (MFR), was used. Moreover, the film was stretched to 5 timesthe initial length in the longitudinal direction and 11 times theinitial length in the transverse direction.

[0394] The results are shown in Tables 3 and 4. The resulting film had alow Young's modulus in the longitudinal direction, and poor tensionresistance and converting ability.

Comparative Example 12

[0395] A biaxially stretched polypropylene film of COMPARATIVE EXAMPLE12 having a thickness of 15 μm was prepared as in EXAMPLE 5 except thatunhydrogenated gum rosin having Tg of 39° C. and a bromine number of 15cg/g and containing polar carboxyl groups that have poor compatibilitywith the polypropylene was used instead of the petroleum resinsubstantially containing no polar-group. Moreover, the film wasstretched to 5 times the initial length in the longitudinal directionand 11 times the initial length in the transverse direction.

[0396] The results are shown in Tables 3 and 4. The resulting film had alow Young's modulus in the longitudinal direction, and poor tensionresistance and converting ability.

Comparative Example 13

[0397] A uniaxially stretched polypropylene film of COMPARATIVE EXAMPLE13 having a thickness of 15 μm was prepared as in COMPARATIVE EXAMPLE 1except that the film was stretched to 8 times the initial length in thelongitudinal direction and was directly wounded right after cooling.

[0398] The results are shown in Tables 3 and 4. The film readily splitalong lines parallel to the longitudinal direction, had poor handlingconvenience, and poor converting ability. TABLE 3 Characteristics ofpolypropylene resin Characteristics of HMS-PP resin MS MFR−0.61log(MFR) + formula (1) Content (cN) (g/10 min) log(MS) 0.82satisfied? (wt. %) COMPARATIVE — — — — — — EXAMPLE 1 COMPARATIVE — — — —— — EXAMPLE 2 COMPARATIVE — — — — — — EXAMPLE 3 COMPARATIVE — — — — — —EXAMPLE 4 COMPARATIVE — — — — — — EXAMPLE 5 COMPARATIVE — — — — — —EXAMPLE 6 COMPARATIVE — — — — — — EXAMPLE 7 COMPARATIVE — — — — — —EXAMPLE 8 COMPARATIVE — — — — — — EXAMPLE 9 COMPARATIVE — — — — — —EXAMPLE 10 COMPARATIVE 20.0 3.0 1.30 0.53 Yes 100 EXAMPLE 11 COMPARATIVE20.0 3.0 1.30 0.53 Yes  10 EXAMPLE 12 COMPARATIVE — — — — — — EXAMPLE 13Characteristics of polypropylene resin Meso pentad MS MFR−0.61log(MFR) + formula (2) fraction (cN) (g/10 min) log(MS) 0.52satisfied? (%) COMPARATIVE 1.5 2.3 0.18 0.30 No 92.0 EXAMPLE 1COMPARATIVE 1.5 2.3 0.18 0.30 No 92.0 EXAMPLE 2 COMPARATIVE 1.1 3.0 0.040.23 No 97.5 EXAMPLE 3 COMPARATIVE 0.6 6.0 −0.22   0.05 No 99.8 EXAMPLE4 COMPARATIVE 1.5 2.3 0.18 0.30 No 92.0 EXAMPLE 5 COMPARATIVE 1.5 2.30.18 0.30 No 92.0 EXAMPLE 6 COMPARATIVE 1.5 2.3 0.18 0.30 No 92.0EXAMPLE 7 COMPARATIVE 1.5 2.3 0.18 0.30 No 92.0 EXAMPLE 8 COMPARATIVE1.5 2.3 0.18 0.30 No 92.0 EXAMPLE 9 COMPARATIVE 1.5 2.3 0.18 0.30 No92.0 EXAMPLE 10 COMPARATIVE 20.0  3.0 1.30 0.23 Yes 97.0 EXAMPLE 11COMPARATIVE 3.0 2.3 0.48 0.30 Yes 92.5 EXAMPLE 12 COMPARATIVE 1.5 2.30.18 0.30 No 92.0 EXAMPLE 13 Content Petroleum resin and ContentStretching ratio (wt. %) terpene resin (wt. %) (longitudinal ×transverse) COMPARATIVE 100 — — 5 × 10 EXAMPLE 1 COMPARATIVE 100 — — 7 ×— EXAMPLE 2 COMPARATIVE 100 — —  (5 × 13) EXAMPLE 3 COMPARATIVE 100 — —5 × — EXAMPLE 4 COMPARATIVE 97 hydrogenated  3 5 × 9 EXAMPLE 5dicyclopentadiene COMPARATIVE 97 hydrogenated  3 (7 × 8) EXAMPLE 6dicyclopentadiene COMPARATIVE 97 hydrogenated  3 8 × — EXAMPLE 7dicyclopentadiene COMPARATIVE 90 hydrogenated 10 5 × 9 EXAMPLE 8dicyclopentadiene COMPARATIVE 90 hydrogenated 10 (8 × 7) EXAMPLE 9dicyclopentadiene COMPARATIVE 90 hydrogenated 10 9 × — EXAMPLE 10dicyclopentadiene COMPARATIVE 100 — —  5 × 12 EXAMPLE 11 COMPARATIVE 95unhydrogenated gum  5  5 × 11 EXAMPLE 12 rosin COMPARATIVE 100 — — 8 × —EXAMPLE 13

[0399] TABLE 4 Young's Young's modulus modulus F2 value F5 value(longitudinal) (transverse) m value at (longitudinal) (longitudinal) at25° C. at 25° C. 25° C. at 25° C. at 25° C. (GPa) (GPa) (−) (MPa) (MPa)COMPARATIVE 1.8 3.7 0.33 33 40 EXAMPLE 1 COMPARATIVE — — — — — EXAMPLE 2COMPARATIVE — — — — — EXAMPLE 3 COMPARATIVE — — — — — EXAMPLE 4COMPARATIVE 2.1 4.0 0.34 38 47 EXAMPLE 5 COMPARATIVE — — — — — EXAMPLE 6COMPARATIVE — — — — — EXAMPLE 7 COMPARATIVE 2.6 4.5 0.37 42 51 EXAMPLE 8COMPARATIVE — — — — — EXAMPLE 9 COMPARATIVE — — — — — EXAMPLE 10COMPARATIVE 1.7 2.1 0.45 41 50 EXAMPLE 11 COMPARATIVE 1.9 4.2 0.31 37 44EXAMPLE 12 COMPARATIVE 2.7 1.1 0.71 43 97 EXAMPLE 13 Young's Young'smodulus (longitudinal) at modulus (transverse) at 80° C. (GPa) 80° C.(GPa) m value at 80° C. (−) COMPARATIVE 0.30 0.60 0.33 EXAMPLE 1COMPARATIVE — — — EXAMPLE 2 COMPARATIVE — — — EXAMPLE 3 COMPARATIVE — —— EXAMPLE 4 COMPARATIVE 0.25 0.55 0.31 EXAMPLE 5 COMPARATIVE — — —EXAMPLE 6 COMPARATIVE — — — EXAMPLE 7 COMPARATIVE 0.30 0.45 0.40 EXAMPLE8 COMPARATIVE — — — EXAMPLE 9 COMPARATIVE — — — EXAMPLE 10 COMPARATIVE0.21 0.25 0.46 EXAMPLE 11 COMPARATIVE 0.25 0.55 0.31 EXAMPLE 12COMPARATIVE 0.40 0.15 0.73 EXAMPLE 13 Heat Heat shrinkage shrinkageWater Vapor (longitudinal) at (transverse) Sum of heat permeability 120°C. at 120° C. shrinkage at (g/m²/d/ Converting (%) (%) 120° C. 0.1 mm)ability COMPARATIVE 4.0 2.0 6.0 1.6 Poor EXAMPLE 1 COMPARATIVE — — — — —EXAMPLE 2 COMPARATIVE — — — — — EXAMPLE 3 COMPARATIVE — — — — — EXAMPLE4 COMPARATIVE 3.8 1.2 5.0 1.3 Poor EXAMPLE 5 COMPARATIVE — — — — —EXAMPLE 6 COMPARATIVE — — — — — EXAMPLE 7 COMPARATIVE 4.0 1.5 5.5 0.9Poor EXAMPLE 8 COMPARATIVE — — — — — EXAMPLE 9 COMPARATIVE — — — — —EXAMPLE 10 COMPARATIVE 1.5 0.5 2.0 2.2 Poor EXAMPLE 11 COMPARATIVE 3.11.7 4.8 2.0 Poor EXAMPLE 12 COMPARATIVE 4.0 −0.5   3.5 1.8 Poor EXAMPLE13

[0400] Tables 1 to 4 demonstrate that since the biaxially stretchedpolypropylene film of the present invention comprises a polypropylenewhich comprises a polypropylene having a melt strength (MS) and a meltflow rate (MFR) measured at 230° C. that satisfy formula (1), or apolypropylene which consists of a polypropylene satisfying the formula(2) between the melt strength (MS) and the melt flow rate (MFR), and atleast one additive that has compatibility with the polypropylene and canprovide plasticity during stretching, a film having a high tensionresistance, and superior dimensional stability and moisture-proofproperty can be prepared. Moreover, such a superior quality film can bestably manufactured without process failures such as film breakages byusing a conventional longitudinal-transverse sequential biaxialstretching machine.

Example 16

[0401] To 90 percent by weight of a polypropylene prepared by blending apublicly known polypropylene having a Trouton ratio of 12, a meso pentadfraction (mmmm) of 92%, an isotactic index (II) of 96%, a melt strength(MS) of 1.5 cN, and a melt flow rate (MFR) of 2.3 g/10 min with 5percent by weight of a high-melt-strength polypropylene (HMS-PP) havinga Trouton ratio of 50, a meso pentad fraction (mmmm) of 92%, anisotactic index (II) of 96.5%, a melt strength of 20 cN, and a melt flowrate of 3 g/10 min and containing long-chain branches, 10 percent byweight of polydicyclopentadiene having Tg of 80° C., a bromine number of3 cg/g, and a hydrogenation rate of 99%, which is a petroleum resinsubstantially containing no polar-group, was added as an additive thathas compatibility with the polypropylene and can provide plasticityduring stretching to prepare a resin. To 100 parts by weight of thisresin, 0.15 part by weight of crosslinked particles of apolymethacrylicacid-based polymer (crosslinked PMMA) having an averageparticle size of 2 μm was added as crosslinked organic particles, and0.8 parts by weight of a 1:1 mixture of glycerin fatty acid ester andalkyldiethanolamine fatty acid ester was added as an antistatic agent.The resulting mixture was fed into a twin-screw extruder, was extrudedat 240° C. into a gut-shape, cooled in a 20° C. water bath, and cut intoa 3-mm length by a chip cutter. The resulting chips were dried for 2hours at 100° C., fed into a single-screw extruder, melted at 260° C.,and filtered. The resulting filtered material was extruded from a slitdie and formed into a sheet by winding on a metal drum having atemperature of 25° C.

[0402] This sheet was passed between rolls maintained at 135° C., andpre-heated, and passed between rolls, which had different rotating speedand were maintained at 140° C., so that the sheet is stretched to 9times the initial length in the longitudinal direction. The stretchedsheet was then immediately cooled to room temperature. The stretchedfilm was next fed into a tenter to be pre-heated at 165° C., stretchedin the transverse direction to 7 times the initial length at 160° C.,and heat-set at 160° C. while being relaxed in the transverse directionby 8%. The film was then cooled and wound so as to obtain a biaxiallystretched polypropylene film having a thickness of 15 μm.

[0403] The composition of the raw material and the results of theevaluation of the film characteristics are shown in Tables 5 and 6. Theresulting film had a high Young's modulus in the longitudinal directionand superior tension resistance, dimensional stability, moisture-proofproperty, and converting ability.

Example 17

[0404] A biaxially stretched polypropylene film of EXAMPLE 17 having athickness of 15 μm was prepared as in EXAMPLE 16 except that thestretching ratio in the longitudinal direction was increased to 11.

[0405] The results are shown in Tables 5 and 6. The resulting film had ahigh Young's modulus in the longitudinal direction and superior tensionresistance, dimensional stability, moisture-proof property, andconverting ability.

Example 18

[0406] A biaxially stretched polypropylene film of EXAMPLE 18 having athickness of 15 μm was prepared as in EXAMPLE 1 except that 3 percent byweight of β-pinene having a Tg of 75° C., a bromine number of 4 cg/g,and a hydrogenation rate of 99%, which is a terpene resin substantiallycontaining no polar-group, was added as an additive that hascompatibility with the polypropylene and can provide plasticity duringstretching, and that the film is stretched to 8 times the initial lengthin the longitudinal direction and to 8 times the initial length in thetransverse direction.

[0407] The results are shown in Tables 5 and 6. The resulting film had ahigh Young's modulus in the longitudinal direction and superior tensionresistance, dimensional stability, moisture-proof property, andconverting ability.

Example 19

[0408] A biaxially stretched polypropylene film of EXAMPLE 19 having athickness of 15 μm was prepared as in EXAMPLE 18 except that 8 percentby weight of the additive terpene resin was added.

[0409] The results are shown in Tables 5 and 6. The resulting film had ahigh Young's modulus in the longitudinal direction and superior tensionresistance, dimensional stability, moisture-proof property, andconverting ability.

Example 20

[0410] A biaxially stretched polypropylene film of EXAMPLE 20 having athickness of 15 μm was prepared as in EXAMPLE 16 except that 10 percentby weight of the HMS-PP containing long-chain branches was blended, andthat 5 percent by weight of polydicyclopentadiene was added. Moreover,the film was stretched to 9 times the initial length in the longitudinaldirection and to 7 times the initial length in the transverse direction.

[0411] The results are shown in Tables 5 and 6. The resulting film had ahigh Young's modulus in the longitudinal direction and superior tensionresistance, dimensional stability, moisture-proof property, andconverting ability.

Example 21

[0412] To 85 percent by weight of a HMS-PP having a Trouton ratio of 50,a meso pentad fraction (mmmm) of 97%, an isotactic index (II) of 96.5%,a melt strength (MS) of 20 cN, and a melt flow rate (MFR) of 3 g/10 minand containing long-chain branches, 15 percent by weight of a mixturecontaining β-pinene having a Tg of 75° C., a bromine number of 4 cg/g,and a hydrogenation rate of 99%, and hydrogenated β-dipentene having aTg of 75° C., a bromine number of 3 cg/g, and a hydrogenation rate of99%, which is a terpene resins substantially containing no polar-groupswas added as an additive that has compatibility with the polypropyleneand can provide plasticity during stretching to prepare a resin. To 100parts by weight of this resin, 0.15 parts by weight of crosslinkedparticles of a polystyrene-based polymer (crosslinked PS) having anaverage particle size of 1 μm was added as crosslinked organicparticles, and 0.8 parts by weight of a 1:1 mixture of glycerin fattyacid ester and alkyldiethanolamine fatty acid ester was added as anantistatic agent. The resulting mixture was fed into a twin-screwextruder, was extruded at 240° C. into a gut-shape, cooled in a 20° C.water bath, and cut into a 3-mm length by a chip cutter. The resultingchips were dried for 2 hours at 100° C., fed into a single-screwextruder, melted at 260° C., and filtered. The resulting filteredmaterial was extruded from a slit die and formed into a sheet by windingon a metal drum having a temperature of 30° C.

[0413] This sheet was passed between rolls maintained at 132° C., andpre-heated, and passed between rolls, which had different rotating speedand were maintained at 137° C. so that the sheet is stretched to 8 timesthe initial length in the longitudinal direction. The stretched sheetwas then immediately cooled to room temperature. The stretched film wasnext fed into a tenter to be pre-heated at 165° C., stretched in thetransverse direction to 8 times the initial length at 160° C., andheat-set at 160° C. while being relaxed in the transverse direction by8%. The film was then cooled and wound so as to obtain a biaxiallystretched polypropylene film having a thickness of 15 μm.

[0414] The results are shown in Tables 5 and 6. The resulting film had ahigh Young's modulus in the longitudinal direction and superior tensionresistance, dimensional stability, moisture-proof property, andconverting ability.

Example 22

[0415] A biaxially stretched polypropylene film of EXAMPLE 22 having athickness of 15 μm was prepared as in EXAMPLE 21 except that, to 80percent by weight of a polypropylene prepared by blending a publiclyknown polypropylene having a Trouton ratio of 12, a meso pentad fraction(mmmm) of 92%, an isotactic index (II) of 96%, a melt strength (MS) of1.5 cN, and a melt flow rate (MFR) of 2.3 g/10 min with 5 percent byweight of a HMS-PP having a Trouton ratio of 50, a meso pentad fraction(mmmm) of 97%, an isotactic index (II) of 96.5%, a melt strength of (MS)20 cN, and a melt flow rate (MFR) of 3 g/10 min and containinglong-chain branches, 20 percent by weight of polydicyclopentadienehaving Tg of 80° C., a bromine number of 3 cg/g, and a hydrogenationrate of 99%, which is a petroleum resin substantially containing nopolar-group, was added as an additive that has compatibility with thepolypropylene and can provide plasticity during stretching. Moreover,the film was stretched to 11 times the initial length in thelongitudinal direction and 6 times the initial length in the transversedirection.

[0416] The results are shown in Tables 5 and 6. The resulting film had ahigh Young's modulus in the longitudinal direction and superior tensionresistance, dimensional stability, moisture-proof property, andconverting ability.

Example 23

[0417] A biaxially stretched polypropylene film of EXAMPLE 23 having athickness of 15 μm was prepared as in EXAMPLE 18, except that apolypropylene prepared by blending 15 percent by weight of a HMS-PPhaving a Trouton ratio of 40, a meso pentad fraction (mmmm) of 95%, anisotactic index (II) of 96%, a melt strength (MS) of 15 cN, and a meltflow rate (MFR) of 2.0 g/10 min and containing long-chain branches wasused.

[0418] The results are shown in Tables 5 and 6. The resulting film had ahigh Young's modulus in the longitudinal direction and superior tensionresistance, dimensional stability, moisture-proof property, andconverting ability.

Example 24

[0419] A biaxially stretched polypropylene film of EXAMPLE 24 having athickness of 15 μm was prepared as in EXAMPLE 23 except that 10 percentby weight of the HMS-PP was blended.

[0420] The results are shown in Tables 5 and 6. The resulting film had ahigh Young's modulus in the longitudinal direction and superior tensionresistance, dimensional stability, moisture-proof property, andconverting ability.

Example 25

[0421] A biaxially stretched polypropylene film of EXAMPLE 25 having athickness of 15 μm was prepared as in EXAMPLE 18, except that 5 percentby weight of a HMS-PP having a Trouton ratio of 60, a meso pentadfraction (mmmm) of 94%, an isotactic index (II) of 95.5%, a meltstrength (MS) of 30 cN, and a melt flow rate (MFR) of 2.1 g/10 min andcontaining long-chain branches was blended.

[0422] The results are shown in Tables 5 and 6. The resulting film had ahigh Young's modulus in the longitudinal direction and superior tensionresistance, dimensional stability, moisture-proof property, andconverting ability.

Example 26

[0423] A biaxially stretched polypropylene film of EXAMPLE 26 having athickness of 15 μm was prepared as in EXAMPLE 16, except that 30 percentby weight of the HMS-PP containing long-chain branches was blended.Moreover, the film was stretched to 10 times the initial length in thelongitudinal direction and to 7 times the initial length in thetransverse direction.

[0424] The results are shown in Tables 5 and 6. The resulting film had ahigh Young's modulus in the longitudinal direction and superior tensionresistance, dimensional stability, moisture-proof property, andconverting ability.

Example 27

[0425] A biaxially stretched polypropylene film of EXAMPLE 28 having athickness of 15 μm was prepared as in EXAMPLE 16, except that apolypropylene prepared by blending a publicly known polypropylene havinga Trouton ratio of 10, a meso pentad fraction (mmmm) of 98%, anisotactic index (II) of 99%, a melt strength (MS) of 1 cN, and a meltflow rate (MFR) of 3.1 g/10 min with 5 percent by weight of the HMS-PPwas used. Moreover, the film was stretched to 10 times in thelongitudinal direction and to 8 times the initial length in thetransverse direction.

[0426] The results are shown in Tables 5 and 6. The resulting film had ahigh Young's modulus in the longitudinal direction and superior tensionresistance, dimensional stability, moisture-proof property, andconverting ability.

Example 28

[0427] A biaxially stretched polypropylene film of EXAMPLE 28 having athickness of 15 μm was prepared as in EXAMPLE 20, except that apolypropylene prepared by blending a publicly known polypropylene havinga Trouton ratio of 11, a meso pentad fraction (mmmm) of 95.5%, anisotactic index (II) of 96%, a melt strength (MS) of 1.3 cN, and a meltflow rate (MFR) of 2.5 g/10 min with 10 percent by weight of the HMS-PPwas blended. Moreover, the film was stretched to 9 times the initiallength in the longitudinal direction and to 8 times the initial lengthin the transverse direction.

[0428] The results are shown in Tables 5 and 6. The resulting film had ahigh Young's modulus in the longitudinal direction and superior tensionresistance, dimensional stability, moisture-proof property, andconverting ability.

Example 29

[0429] A biaxially stretched polypropylene film of COMPARABLE EXAMPLE 29having a thickness of 15 μm was prepared as in EXAMPLE 19 except thatstretching in the longitudinal direction was performed in two steps,i.e., the film was preheated at 135° C., stretched to 1.5 times theinitial length at 137° C. in the first step, and stretched to 5.3 timesthe initial length at 142° C. in the second step.

[0430] The results are shown in Tables 5 and 6. The resulting film had ahigh Young's modulus in the longitudinal direction and superior tensionresistance, dimensional stability, moisture-proof property, andconverting ability. TABLE 5 Characteristics of polypropylene resinCharacteristics of HMS-PP resin Trouton Content Trouton ratio of Mesopentad fraction of PP ratio (wt. %) PP as a whole as a whole (%) EXAMPLE16 50 5 22 92.3 EXAMPLE 17 50 5 22 92.3 EXAMPLE 18 50 5 22 92.3 EXAMPLE19 50 5 22 92.3 EXAMPLE 20 50 10 26 92.5 EXAMPLE 21 50 100 50 97.0EXAMPLE 22 50 5 22 92.3 EXAMPLE 23 40 15 18 92.5 EXAMPLE 24 40 10 1392.3 EXAMPLE 25 60 5 30 92.1 EXAMPLE 26 50 30 36 93.5 EXAMPLE 27 50 5 1998.0 EXAMPLE 28 50 10 25 95.6 EXAMPLE 29 50 5 22 92.3 Content Petroleumresin and terpene Content Stretching ratio (wt. %) resin (wt. %)(longitudinal × transverse) EXAMPLE 16 90 hydrogenated 10 9 × 7dicyclopentadiene EXAMPLE 17 90 hydrogenated 10 11 × 6 dicyclopentadiene EXAMPLE 18 97 hydrogenated β-pinene 3 8 × 8 EXAMPLE 1992 hydrogenated β-pinene 8 8 × 8 EXAMPLE 20 95 hydrogenated 5 9 × 7dicyclopentadiene EXAMPLE 21 85 hydrogenated β-pinene and 15 8 × 8hydrogenated β-dipentene EXAMPLE 22 80 hydrogenated 20 11 × 6 dicyclopentadiene EXAMPLE 23 97 hydrogenated β-pinene 3 8 × 8 EXAMPLE 2497 hydrogenated β-pinene 3 8 × 8 EXAMPLE 25 97 hydrogenated β-pinene 3 8× 8 EXAMPLE 26 90 hydrogenated 10 10 × 7  dicyclopentadiene EXAMPLE 2790 hydrogenated 10 10 × 8  dicyclopentadiene EXAMPLE 28 hydrogenated 5 9× 8 dicyclopentadiene EXAMPLE 29 92 hydrogenated β-pinene 8 (1.5 * 5.3)× 9

[0431] TABLE 6 Young's Young's modulus modulus F2 value F5 value(longitudinal) (transverse) at m value at (longitudinal) (longitudinal)at 25° C. 25° C. 25° C. at 25° C. at 25° C. (GPa) (GPa) (−) (MPa) (MPa)EXAMPLE 16 3.9 3.8 0.51 67 95 EXAMPLE 17 4.4 3.4 0.56 75 110 EXAMPLE 183.1 4.0 0.44 48 62 EXAMPLE 19 3.8 3.9 0.49 63 81 EXAMPLE 20 3.3 3.4 0.4953 78 EXAMPLE 21 3.8 3.9 0.49 69 92 EXAMPLE 22 5.0 3.2 0.61 76 115EXAMPLE 23 2.9 4.0 0.42 46 58 EXAMPLE 24 2.7 4.3 0.39 42 54 EXAMPLE 253.4 3.6 0.49 51 73 EXAMPLE 26 4.2 3.1 0.58 69 101 EXAMPLE 27 4.0 4.20.49 70 90 EXAMPLE 28 3.5 4.3 0.45 58 68 EXAMPLE 29 4.2 4.4 0.49 65 94Young's modulus Young's modulus (transverse) at 80° C. (longitudinal) at80° C. (GPa) (GPa) m value at 80° C. (−) EXAMPLE 16 0.62 0.62 0.50EXAMPLE 17 0.67 0.60 0.53 EXAMPLE 18 0.50 0.55 0.48 EXAMPLE 19 0.63 0.630.50 EXAMPLE20 0.53 0.53 0.50 EXAMPLE 21 0.59 0.59 0.50 EXAMPLE 22 0.780.65 0.55 EXAMPLE 23 0.48 0.60 0.44 EXAMPLE 24 0.43 0.58 0.43 EXAMPLE 250.55 0.55 0.50 EXAMPLE 26 0.67 0.63 0.52 EXAMPLE 27 0.75 0.75 0.50EXAMPLE 28 0.68 0.76 0.47 EXAMPLE 29 0.62 0.65 0.49 Heat Heat shrinkageshrinkage (longitudinal) (transverse) Sum of heat Water vapor at 120° C.at 120° C. shrinkage at permeability Converting (%) (%) 120° C.(g/m²/d/0.1 mm) ability EXAMPLE 16 3.7 1.1 4.8 0.7 Good EXAMPLE 17 4.31.1 5.4 0.6 Good EXAMPLE 18 2.8 1.0 3.8 1.2 Good EXAMPLE 19 3.0 1.1 4.10.9 Good EXAMPLE20 3.2 1.0 4.2 1.1 Good EXAMPLE 21 3.2 1.6 4.8 0.7 GoodEXAMPLE 22 4.0 1.3 5.3 0.5 Good EXAMPLE 23 2.8 1.0 3.8 1.2 Good EXAMPLE24 3.0 1.1 4.1 1.2 Good EXAMPLE 25 2.7 0.8 3.5 1.2 Good EXAMPLE 26 3.31.2 4.5 0.7 Good EXAMPLE 27 1.9 0.6 2.5 0.5 Good EXAMPLE 28 1.5 0.0 1.50.7 Good EXAMPLE 29 4.0 1.5 5.5 0.9 Good

Comparative Examples 1 to 4, and 11 to 13

[0432] The films of COMPARATIVE EXAMPLE 1 to 4, and 11 to 13 are shownin Tables 7 and 8.

Comparative Example 14

[0433] A biaxially stretched polypropylene film of COMPARATIVE EXAMPLE14 having a thickness of 15 μm was prepared as in COMPARATIVE EXAMPLE 1except that 3 percent by weight of β-pinene having a Tg of 75° C., abromine number of 4 cg/g, and a hydrogenation rate of 99%, which is aterpene resin substantially containing no polar-group, as an additivethat has compatibility with the polypropylene and can provide plasticityduring stretching, was added to 97 percent by weight of polypropylene,and that the film was stretched to 5 times the initial length in thelongitudinal direction and to 9 times the initial length in thetransverse direction.

[0434] The results are shown in Tables 7 and 8. The resulting film hadlow Young's modulus in the longitudinal direction, insufficient tensionresistance, and poor converting ability.

Comparative Example 15

[0435] A biaxially stretched polypropylene film of COMPARATIVE EXAMPLE15 having a thickness of 15 μm was prepared as in COMPARATIVE EXAMPLE 14except that the film was stretched to 7 times the initial length in thelongitudinal direction and to 8 times the initial length in thetransverse direction.

[0436] The results are shown in Tables 7 and 8. Because film breakageoccurred during transverse stretching, a film having a sufficient lengthcould not be obtained. The resulting film was not suited for industrialproduction.

Comparative Example 16

[0437] A biaxially stretched polypropylene film of COMPARATIVE EXAMPLE16 having a thickness of 15 μm was prepared as in COMPARATIVE EXAMPLE 14except that the stretching ratio in the longitudinal direction wasincreased to 8.

[0438] The results are shown in Tables 7 and 8. Because significantdegree of film breakage occurred during transverse stretching, asufficient film could not be obtained.

Comparative Example 17

[0439] A biaxially stretched polypropylene film of COMPARATIVE EXAMPLE17 having a thickness of 15 μm was prepared as in COMPARATIVE EXAMPLE 14except that 10 percent by weight of β-pinene was added.

[0440] The results are shown in Tables 7 and 8. The film had a lowYoung's modulus in the longitudinal direction at 80° C., insufficienttension resistance, and poor dimensional stability and convertingability.

Comparative Example 18

[0441] A biaxially stretched polypropylene film of COMPARATIVE EXAMPLE18 having a thickness of 15 μm was prepared as in COMPARATIVE EXAMPLE 17except that the film was stretched to 8 times the initial length in thelongitudinal direction and to 7 times the initial length in thetransverse direction.

[0442] The results are shown in Tables 7 and 8. Because film breakageoccurred during transverse stretching, a film having a sufficient lengthcould not be obtained. The resulting film was not suited for industrialproduction.

Comparative Example 19

[0443] A biaxially stretched polypropylene film of COMPARATIVE EXAMPLE19 having a thickness of 15 μm was prepared as in COMPARATIVE EXAMPLE 17except that the stretching ratio in the longitudinal direction wasincreased to 9.

[0444] The results are shown in Tables 7 and 8. Because significantdegree of film breakage occurred during transverse stretching, asufficient film could not be obtained. TABLE 7 Characteristics ofpolypropylene resin Characteristics of HMS-PP resin Meso pentad fractionof Trouton Content Trouton ratio of PP as a whole ratio (wt. %) PP as awhole (%) COMPARATIVE — — 12 92.0 EXAMPLE 1 COMPARATIVE — — 12 92.0EXAMPLE 2 COMPARATIVE — — 10 97.5 EXAMPLE 3 COMPARATIVE — — 8 99.8EXAMPLE 4 COMPARATIVE 50 100 50 97.0 EXAMPLE 11 COMPARATIVE 50  10 2692.5 EXAMPLE 12 COMPARATIVE — — 12 92.0 EXAMPLE 13 COMPARATIVE — — 1292.0 EXAMPLE 14 COMPARATIVE — — 12 92.0 EXAMPLE 15 COMPARATIVE — — 1292.0 EXAMPLE 16 COMPARATIVE — — 12 92.0 EXAMPLE 17 COMPARATIVE — — 1292.0 EXAMPLE 18 COMPARATIVE — — 12 92.0 EXAMPLE 19 Content Petroleumresin Content Stretching ratio (wt. %) and terpene resin (wt. %)(longitudinal × transverse) COMPARATIVE 100 — —  5 × 10 EXAMPLE 1COMPARATIVE 100 — — 7 × — EXAMPLE 2 COMPARATIVE 100 — —  (5 × 13)EXAMPLE 3 COMPARATIVE 100 — — 5 × — EXAMPLE 4 COMPARATIVE 100 — —  5 ×12 EXAMPLE 11 COMPARATIVE 95 unhydrogenated 5  5 × 11 EXAMPLE 12 gumrosin COMPARATIVE 100 — — 8 × — EXAMPLE 13 COMPARATIVE 97 hydrogenated 35 × 9 EXAMPLE 14 β-pinene COMPARATIVE 97 hydrogenated 3 (7 × 8) EXAMPLE15 β-pinene COMPARATIVE 90 hydrogenated 10 5 × 9 EXAMPLE 16 β-pineneCOMPARATIVE 90 hydrogenated 10 5 × 9 EXAMPLE 17 β-pinene COMPARATIVE 90hydrogenated 10 (8 × 7) EXAMPLE 18 β-pinene COMPARATIVE 90 hydrogenated10 9 × — EXAMPLE 19 β-pinene

[0445] TABLE 8 Young's Young's modulus modulus F2 value F5 value(longitudinal) (transverse) m value at (longitudinal) (longitudinal) at25° C. at 25° C. 25° C. at 25° C. at 25° C. (GPa) (GPa) (−) (MPa) (MPa)COMPARATIVE 1.8 3.7 0.33 33 40 EXAMPLE 1 COMPARATIVE — — — — — EXAMPLE 2COMPARATIVE — — — — — EXAMPLE 3 COMPARATIVE — — — — — EXAMPLE 4COMPARATIVE 1.7 2.1 0.45 41 50 EXAMPLE 11 COMPARATIVE 1.9 4.2 0.31 37 44EXAMPLE 12 COMPARATIVE 2.7 1.1 0.71 43 97 EXAMPLE 13 COMPARATIVE 2.1 4.00.34 38 45 EXAMPLE 14 COMPARATIVE — — — — — EXAMPLE 15 COMPARATIVE — — —— — EXAMPLE 16 COMPARATIVE 2.4 4.7 0.34 40 49 EXAMPLE 17 COMPARATIVE — —— — — EXAMPLE 18 COMPARATIVE — — — — — EXAMPLE 19 Young's modulusYoung's modulus (longitudinal) at 80° C. (transverse) at 80° C. (GPa)(GPa) m value at 80° C. (−) COMPARATIVE 0.30 0.60 0.33 EXAMPLE 1COMPARATIVE — — — EXAMPLE 2 COMPARATIVE — — — EXAMPLE 3 COMPARATIVE — —— EXAMPLE 4 COMPARATIVE 0.21 0.25 0.46 EXAMPLE 11 COMPARATIVE 0.25 0.550.31 EXAMPLE 12 COMPARATIVE 0.40 0.15 0.73 EXAMPLE 13 COMPARATIVE 0.280.55 0.34 EXAMPLE 14 COMPARATIVE — — — EXAMPLE 15 COMPARATIVE — — —EXAMPLE 16 COMPARATIVE 0.28 0.50 0.36 EXAMPLE 17 COMPARATIVE — — —EXAMPLE 18 COMPARATIVE — — — EXAMPLE 19 Heat Heat Sum of shrinkageshrinkage heat (longitudinal) (transverse) shrinkage Water vapor at 120°C. at 120° C. at permeability Converting (%) (%) 120° C. (g/m²/d/0.1 mm)ability COMPARATIVE 4.0 2.0 6.0 1.6 Poor EXAMPLE 1 COMPARATIVE — — — — —EXAMPLE 2 COMPARATIVE — — — — — EXAMPLE 3 COMPARATIVE — — — — — EXAMPLE4 COMPARATIVE 1.5 0.5 2.0 2.2 Poor EXAMPLE 11 COMPARATIVE 3.1 1.7 4.82.0 Poor EXAMPLE 12 COMPARATIVE 4.0 −0.5   3.5 1.8 Poor EXAMPLE 13COMPARATIVE 4.0 1.0 5.0 1.4 Poor EXAMPLE 14 COMPARATIVE — — — — —EXAMPLE 15 COMPARATIVE — — — — — EXAMPLE 16 COMPARATIVE 4.2 1.8 6.0 1.0Poor EXAMPLE 17 COMPARATIVE — — — — — EXAMPLE 18 COMPARATIVE — — — — —EXAMPLE 19

[0446] Tables 5 to 8 demonstrate that since the biaxially stretchedpolypropylene film of the present invention comprises a polypropylenewhich comprises a polypropylene having a Trouton ratio of 30 or more ora polypropylene which consists of a polypropylene having a Trouton ratioof 16 or more, and at least one additive that has compatibility with thepolypropylene and can provide plasticity during stretching, a filmhaving a high tension resistance, and superior dimensional stability andmoisture-proof property can be prepared. Moreover, such a superiorquality film can be stably manufactured without process failures such asfilm breakages by using a conventional longitudinal-transversesequential biaxial stretching machine.

Example 30

[0447] A biaxially stretched polypropylene film of EXAMPLE 30 having athickness of 15 μm was prepared as in EXAMPLE 3 except that thetemperature of the cooling drum was increased to 80° C. to prepare theunstretched sheet. The results of evaluation of the film characteristicsare shown in Table 9.

Comparative Example 20

[0448] A biaxially stretched polypropylene film of COMPARATIVE EXAMPLE20 having a thickness of 15 μm was prepared as in COMPARATIVE EXAMPLE 1except that the temperature of the cooling drum was increased to 80° C.to prepare the unstretched sheet. The results of evaluation of the filmcharacteristics are shown in Table 9. TABLE 9 Young's Young's modulusmodulus F2 value F5 value (longitudinal) (transverse) m value at(longitudinal) (longitudinal) at 25° C. at 25° C. 25° C. at 25° C. at25° C. (GPa) (GPa) (−) (MPa) (MPa) EXAMPLE 30 4.0 3.5 0.53 63 88COMPARATIVE 1.9 3.9 0.33 33 41 EXAMPLE 20 Young's modulus Young'smodulus (longitudinal) at 80° C. (transverse) at 80° C. (GPa) (GPa) mvalue at 80° C. (−) EXAMPLE 30 0.70 0.50 0.58 COMPARATIVE 0.30 0.60 0.33EXAMPLE 20 Heat Heat Sum of shrinkage shrinkage heat (longitudinal)(transverse) shrinkage Water vapor at 120° C. at 120° C. at 120° C.permeability Converting (%) (%) (%) (g/m²/d/0.1 mm) ability EXAMPLE 302.7 0.3 3.0 1.0 Good COMPARATIVE 3.9 1.8 5.7 1.6 Poor EXAMPLE 20

[0449] Observation Results of Fibril Structures of Examples 1, 3, 17,19, and 30, and Comparative Examples 1, 5, 17 and 20

[0450] The fibril structure of each of the films of EXAMPLES 1, 3, 17,19, and 30, and COMPARATIVE EXAMPLES 1, 5, 17 and 20 described above wasobserved by using an atomic force microscope (AFM).

[0451] The observation results of the fibril structures are shown inTable 10. The films of the present invention contained longitudinalfibrils that rarely deform against applied stresses, resulting in a filmhaving a superior tension resistance. Moreover, the handling convenienceduring converting process was also superior because the formula belowbetween Young's modulus in the longitudinal direction Y(MD) at 25° C.and the heat shrinkage in the longitudinal direction S(MD) at 120° C.was satisfied:

Y(MD)≧S(MD)−1

[0452] Accordingly, a film having such superior characteristics can bestably manufactured. Moreover, the number of the fibrils and the widthof the fibrils were controllable by adjusting the film-formingconditions such as the temperature of the cooling drum. In contrast,conventional films of the COMPARATIVE EXAMPLES did not containlongitudinal fibrils, and the fibril structures readily deformed againstapplied stresses, resulting in a film having low tension resistance, andbecause the films did not satisfy the above-described formula, exhibitedpoor converting ability. Furthermore, no longitudinal fibrils wereobtained even when the film-forming conditions were altered. TABLE 10Average Presence of width of No. of longitudinal longitudinallongitudinal formula fibrils fibrils fibrils (5) EXAMPLE 1 A 75 3Satisfied EXAMPLE 3 C 59 2 Satisfied EXAMPLE 17 A 120 5 SatisfiedEXAMPLE 19 B 70 2 Satisfied EXAMPLE 30 A 72 3 Satisfied COMPARATIVE NONE— — Not EXAMPLE 1 satisfied COMPARATIVE NONE — — Not EXAMPLE 5 satisfiedCOMPARATIVE NONE — — Not EXAMPLE 17 satisfied COMPARATIVE NONE — — NotEXAMPLE 20 satisfied

Example 31

[0453] A biaxially stretched polypropylene film was prepared by biaxialstretching as in EXAMPLE 3 except that the antistatic agent was notadded and that the amount of the crosslinked particles of apolymethacrylicacid-based copolymer (crosslinked PMMA) having an averageparticle size of 2μm was changed to 0.05 parts by weight. Subsequently,one side of the film was subjected to corona discharge treatment in anatmosphere containing 15% of carbon dioxide gas and 85% of nitrogen gasto obtain a biaxially stretched polypropylene film with a surfacewetting tension of 45 mN/m. The biaxially stretched polypropylene filmwas then installed in a vacuum metallization apparatus. While the filmwas allowed to run, aluminum metal was heated, melted, and evaporated sothat a layer having a thickness of 30 nm was deposited on the side thathad been subjected to corona discharge treatment. Thus, a metallizedbiaxially stretched polypropylene film was obtained.

[0454] The gas barrier properties of the metallized biaxially stretchedpolypropylene film were as follows: oxygen permeability: 200ml/m².d.MPa; and water vapor permeability: 0.2 g/m².d. The gas barrierproperty after converting process was as follows: oxygen permeability:205 ml/m².d.MPa; and water vapor permeability: 0.2 g/m².d. Nosignificant change in gas barrier properties was observed.

Example 32

[0455] A biaxially stretched polypropylene film was prepared as inEXAMPLE 5, except that the antistatic agent and the crosslinked PMMAparticles were not added and that 0.05 parts by weight of crosslinkedsilicon particles having an average particle size of 2 μm were added.Then metallized biaxially stretched polypropylene film was prepared asin EXAMPLE 31.

[0456] The gas barrier properties of the metallized biaxially stretchedpolypropylene film were as follows: oxygen permeability: 150ml/m².d.MPa; and water vapor permeability: 0.15 g/m².d. The gas barrierproperties, i.e., the oxygen permeability and the water vaporpermeability, after converting process were the same as those beforeconverting.

Example 33

[0457] A biaxially stretched polypropylene film was prepared as inEXAMPLE 16, except that the antistatic agent was not added and that 0.02parts by weight of crosslinked PMMA particles having an average particlesize of 2 μm were added. Then metallized biaxially stretchedpolypropylene film was prepared as in EXAMPLE 31.

[0458] The gas barrier properties of the metallized biaxially stretchedpolypropylene film were as follows: oxygen permeability: 130ml/m².d.MPa; and water vapor permeability: 0.13 g/m².d.MPa. The gasbarrier properties, i.e., the oxygen permeability and the water vaporpermeability, after converting process were the same as those beforeconverting.

Example 34

[0459] In EXAMPLE 26, a metallized biaxially stretched polypropylenefilm was prepared as in EXAMPLE 33.

[0460] The gas barrier properties of the metallized biaxially stretchedpolypropylene film were as follows: oxygen permeability: 100ml/m².d.MPa; and water vapor permeability: 0.1 g/m².d. The gas barrierproperties, i.e., the oxygen permeability and the water vaporpermeability, after converting process were the same as those beforeconverting.

Comparative Example 21

[0461] A biaxially stretched polypropylene film was prepared as inCOMPARATIVE EXAMPLE 1 except that the antistatic agent was not added andthat the amount of the crosslinked particles of apolymethacrylicacid-based copolymer (crosslinked PMMA) having an averageparticle size of 2 μm was changed to 0.05 part by weight as in EXAMPLE31. Using this film, a metallized biaxially stretched polypropylene filmwas obtained as in EXAMPLE 31.

[0462] The gas barrier properties of the metallized biaxially stretchedpolypropylene film were as follows: oxygen permeability: 300ml/m².d.MPa; and water vapor permeability: 0.25 g/m².d. The metallizedbiaxially stretched polypropylene film had low Young's modulus in thelongitudinal direction, insufficient tension resistance, and poorconverting ability. The gas barrier properties after converting processwere as follows: oxygen permeability: 620 ml/m².d.MPa; and water vaporpermeability: 0.23 g/m².d. The oxygen permeability dramatically degradedafter converting.

Comparative Example 22

[0463] In COMPARATIVE EXAMPLE 8, a metallized biaxially stretchedpolypropylene film was prepared as in EXAMPLE 31. The gas barrierproperties of the metallized biaxially stretched polypropylene film wereas follows: oxygen permeability: 270 ml/m².d.MPa; and water vaporpermeability: 0.28 g/m².d.

[0464] The metallized biaxially stretched polypropylene film had a lowYoung's modulus at high temperature, i.e., 80° C., insufficient tensionresistance, and poor converting ability. The gas barrier propertiesafter converting process were as follows: oxygen permeability: 680ml/m².d.MPa; and water vapor permeability: 0.23 g/m².d. The oxygenpermeability dramatically degraded after converting.

Example 35

[0465] The resin composition as in EXAMPLE 3 but without the antistaticagent and with 0.05 part by weight of crosslinked particles of thepolymethacrylicacid-based polymer (crosslinked PMMA) was extruded andformed into a sheet as in EXAMPLE 3 to prepare a core layer. The sheetwas stretched in the longitudinal direction to 8 times the initiallength as in EXAMPLE 1, and the surface of the film stretched to 8 timeswas subjected to corona discharge treatment in air so as to obtain asurface wetting tension of 37 mN/m. A blended coating materialcontaining 100 parts by weight of “Hydran” AP-40F (manufactured byDainippon Ink and Chemicals, Inc., solid content: 30%) as awater-dispersible polyesterpolyurethane-based resin, 15 parts by weightof N-methylpyrrolidone as a water-soluble organic solvent, and 5 partsby weight of a melamine compound, i.e., “Beckamine” APM (manufactured byDainippon Ink and Chemicals, Inc.) as a crosslinking agent, and 2 partsby weight of a water-soluble acidic compound, i.e., “Catalyst” PTS(manufactured by Dainippon Ink and Chemicals, Inc.) as a crosslinkingaccelerator was applied on this treated surface by a coating bar to forma coating layer. Subsequently, the coated film was stretched in thetransverse direction as in EXAMPLES so as to prepare a biaxiallystretched polypropylene film. The film thickness construction wascoating layer/core layer=0.2 μm/15 μm. The adhesive strength between thesurface of the film of the present invention and the coating layer was2.3 N/cm, the centerline average roughness Ra of the coating layer was0.03 μm, and the surface gloss was 140%.

[0466] Next, the biaxially stretched polypropylene film was installed ina vacuum metallizing apparatus, and aluminum metal was heated, melted,and evaporated so that the evaporated aluminum cohere and deposit on thefilm surface to make a metallization layer. Thus, a metallized biaxiallystretched polypropylene film was obtained.

[0467] The gas barrier properties of the metallized biaxially stretchedpolypropylene film were as follows: oxygen permeability: 20 ml/m².d.MPa;and water vapor permeability: 0.07 g/m².d. The adhesive strength betweenthe coating layer and the metallization layer was 1.7 N/cm. The gasbarrier properties after converting process were maintained as high asthose before converting and were as follows: oxygen permeability 22ml/m².d.MPa; and water vapor permeability: 0.07 g/m².d.

Example 36

[0468] A biaxially stretched polypropylene film provided with a coatinglayer having a thickness of 0.2 μm was prepared as in EXAMPLE 35 exceptthat a blended coating material containing 100 parts by weight of“Hydran” AP-40F (manufactured by Dainippon Ink and Chemicals, Inc.,solid content: 30%) as a water-dispersible polyesterpolyurethane-basedresin, 5 parts by weight of a melamine compound, i.e., “Beckamine” APM(manufactured by Dainippon Ink and Chemicals, Inc.) as a crosslinkingagent, and 2 parts by weight of a water-soluble acidic compound, i.e.,“Catalyst” PTS (manufactured by Dainippon Ink and Chemicals, Inc.) as acrosslinking accelerator was coated using the coating bar. The adhesivestrength between the surface of the film of the present invention andthe coating layer was 2.0 N/cm, the centerline average roughness Ra ofthe coating layer was 0.03 μm, and the glossiness was 138%.

[0469] Next, an aluminum metallization layer was formed on the biaxiallystretched polypropylene film as in EXAMPLE 34 so as to obtain ametallized biaxially stretched polypropylene film.

[0470] The gas barrier properties of the metallized biaxially stretchedpolypropylene film were as follows: oxygen permeability: 30 ml/m².d.MPa;and water vapor permeability: 0.08 g/m².d. The adhesive strength betweenthe coating layer and the metallization layer was 1.5 N/cm. The gasbarrier properties after converting process were maintained as high asthose before converting and were as follows: oxygen permeability 32ml/m².d.MPa; and water vapor permeability: 0.09 g/m².d.

EXAMPLE 37

[0471] The surface of the biaxially stretched polypropylene film ofEXAMPLE 16 was subjected to corona discharge treatment in air so as toobtain a surface wetting tension of 37 mN/m, and the blended coatingmaterial of EXAMPLE 34 was applied on this treated surface using anoff-line gravure coater to form a coating layer having a thickness of0.2 μm. The film was wound and subjected to aluminum metallization as inEXAMPLE 35 to obtain a metallized biaxially stretched polypropylenefilm.

[0472] The gas barrier properties of the metallized biaxially stretchedpolypropylene film were as follows: oxygen permeability: 10 ml/m².d.MPa;and water vapor permeability: 0.08 g/m².d. The adhesive strength betweenthe biaxially stretched polypropylene film and the coating layer was 3N/cm, and the adhesive strength between the coating layer and themetallization layer was 2 N/cm. The gas barrier properties afterconverting process were maintained as high as those before convertingand were as follows: oxygen permeability 12 ml/m².d.MPa; and water vaporpermeability: 0.08 g/m².d.

Example 38

[0473] A biaxially stretched polypropylene film was prepared as inEXAMPLE 26 but without adding the antistatic agent and the particles anda coating layer was formed as in EXAMPLE 35. Subsequently, a metallizedbiaxially stretched polypropylene film was prepared as in EXAMPLE 35.

[0474] The gas barrier properties of the metallized biaxially stretchedpolypropylene film were as follows: oxygen permeability: 8 ml/m².d.MPa;and water vapor permeability: 0.05 g/m².d. The adhesive strength of thecoating layer was 3.2 N/cm, and the adhesive strength between thecoating layer and the metallization layer was 2.5 N/cm. The gas barrierproperties after converting process were maintained as high as thosebefore converting and were as follows: oxygen permeability 8ml/m².d.MPa; and water vapor permeability: 0.05 g/m².d.

Comparative Example 23

[0475] A metallized biaxially stretched polypropylene film was preparedas in EXAMPLE 35 but with a different coating material prepared asfollows. In the presence of a catalyst, 0.12 mol of terephthalic acid,0.84 mol of isophthalic acid, 0.33 mol of diethylene glycol, and 0.65mol of neopentyl glycol were allowed to react at 190 to 220° C. for 6hours while removing distillation water, and the resulting substance wassubjected to condensation reaction for 1 hour at 250° C. in vacuum so asto obtain a prepolymer. The prepolymer was blended with 0.13 mol of5-(2,5dioxotetrahydrofurfryl)-3-methyl-3-cyclohexene-1,2-dicarboxylanhydride so as to perform selective monoesterification reaction at 140°C. for 3 hours to obtain a polymer. Next, the polymer was neutralizedwith ammonia to prepare a polyester resin. To 100 parts by weight ofactive principle of the polyester resin, 10 parts by weight of anisocyanate compound, i.e., hexamethylene diisocyanate as a crosslinkingagent and 1.5 parts by weight of “Catalyst” PTS (manufactured byDainippon Ink and Chemicals, Inc.) as a crosslinking catalyst were addedto prepare the coating material.

[0476] The gas barrier properties of the metallized biaxially stretchedpolypropylene film were as follows: oxygen permeability: 120ml/m².d.MPa; and water vapor permeability: 0.1 g/m².d. The adhesivestrength between the metallized biaxially stretched polypropylene filmand the coating layer was low, and coating layer peeled from the filmduring converting process. Thus, the gas barrier properties weredramatically decreased to an oxygen permeability of 750 ml/m².d.MPa anda water vapor permeability of 0.35 g/m².d.

Comparative Examples 24 and 25

[0477] A metallized biaxially stretched polypropylene film ofCOMPARATIVE EXAMPLE 24 was prepared as in EXAMPLE but with a coatinglayer having a thickness of 0.03 μm. A metallized biaxially stretchedpolypropylene film of COMPARATIVE EXAMPLE 25 was prepared as in EXAMPLE35 but with a coating layer having a thickness of 4 μm.

[0478] In COMPARATIVE EXAMPLE 24, gas barrier properties did not improvedue to the thin coating layer. The oxygen permeability was 195ml/m².d.MPa, and the water vapor permeability was 0.2 g/m².d.

[0479] In COMPARATIVE EXAMPLE 25, the coating layer did not sufficientlycure due to the large thickness of the layer, and the adhesive strengthto the film surface was low. As for the gas barrier properties, theoxygen permeability was 210 ml/m².d.MPa, and the water vaporpermeability was 0.13 g/m².d.

Comparative Example 26

[0480] In COMPARATIVE EXAMPLE 1, a metallized biaxially stretchedpolypropylene film was prepared as in EXAMPLE 35.

[0481] Due to the deposition of the coating layer, the gas barrierproperties of the metallized biaxially stretched polypropylene film wereimproved, i.e., oxygen permeability: 30 ml/m².d.MPa, and water vaporpermeability: 0.15 g/m².d. However, because the metallized biaxiallystretched polypropylene film had a low Young's modulus in thelongitudinal direction and insufficient tension resistance, the gasbarrier properties significantly degraded after converting process,i.e., oxygen permeability: 420 ml/m².d.MPa; and water vaporpermeability: 0.27 g/m².d.

Comparative Example 27

[0482] In COMPARATIVE EXAMPLE 14, a metallized biaxially stretchedpolypropylene film was prepared as in EXAMPLE 35. Due to the coatinglayer, the gas barrier properties of the metallized biaxially stretchedpolypropylene film were improved, i.e., oxygen permeability: 27ml/m².d.MPa, and water vapor permeability: 0.10 g/m².d. However, becausethe metallized biaxially stretched polypropylene film had a low Young'smodulus in the longitudinal direction and insufficient tensionresistance, the gas barrier properties significantly degraded afterconverting process, i.e., oxygen permeability: 370 ml/m².d.MPa; andwater vapor permeability: 0.23 /m².d. TABLE 11 Thickness arrangementAdhesive Adhesive (μm) base Young's modulus strength between strength ofthe layer/coating (longitudinal) at surface and the metallizationlayer/metal- 25° C. coating layer layer lization layer (GPa) (N/cm)(N/cm) EXAMPLE 31 15/—/0.03 3.1 — 0.7 EXAMPLE 32 15/—/0.03 3.6 — 0.6EXAMPLE 33 15/—/0.03 3.9 — 0.7 EXAMPLE 34 15/0.2/0.03 4.2 — 0.7 EXAMPLE35 15/0.2/0.03 3.1 2.3 1.7 EXAMPLE 36 15/0.2/0.03 3.1 2.0 1.5 EXAMPLE 3715/0.2/0.03 3.9 3.0 2.0 EXAMPLE 38 15/0.2/0.03 4.2 3.2 2.5 COMPARATIVE15/—/0.03 2.0 — 0.7 EXAMPLE 21 COMPARATIVE 15/—/0.03 2.6 — 0.7 EXAMPLE22 COMPARATIVE 15/0.2/0.03 3.1 0.7 — EXAMPLE 23 COMPARATIVE 15/0.03/0.033.1 1.5 0.7 EXAMPLE 24 COMPARATIVE 15/4/0.03 3.1 1.0 0.2 EXAMPLE 25COMPARATIVE 15/0.2/0.03 2.0 2.3 1.7 EXAMPLE 26 COMPARATIVE 15/0.2/0.032.1 2.3 1.7 EXAMPLE 27 Oxygen Oxygen Water vapor permeability Watervapor permeability after permeability after after permeability afterconverting converting metallization metallization process process(ml/m²/d/MPa) (g/m²/d) (ml/m²/d/MPa) (g/m²/d) EXAMPLE 31 200 0.20 2050.20 EXAMPLE 32 150 0.15 150 0.15 EXAMPLE 33 130 0.13 130 0.13 EXAMPLE34 100 0.10 100 0.10 EXAMPLE 35 20 0.07 22 0.07 EXAMPLE 36 30 0.08 320.09 EXAMPLE 37 10 0.08 12 0.08 EXAMPLE 38 8 0.05 8 0.05 COMPARATIVE 3000.25 620 0.28 EXAMPLE 21 COMPARATIVE 270 0.22 680 0.23 EXAMPLE 22COMPARATIVE 120 0.10 750 0.35 EXAMPLE 23 COMPARATIVE 195 0.20 200 0.20EXAMPLE 24 COMPARATIVE 210 0.30 220 0.23 EXAMPLE 25 COMPARATIVE 30 0.15420 0.27 EXAMPLE 26 COMPARATIVE 27 0.10 370 0.23 EXAMPLE 27

[0483] The results of the evaluation of the film characteristics areshown in Table 11. Because the biaxially stretched polypropylene film ofthe present invention has high stiffness in the longitudinal direction,degradation in barrier property after converting process can be avoidedwhen the film is used as a base film of a metallized film. Moreover, byforming a coating layer between the base layer and the metallizationlayer, the barrier property can be further enhanced.

[0484] Industrial Applicability

[0485] A biaxially stretched polypropylene film of the present inventionhas an increased stiffness in the longitudinal direction withoutdegrading important characteristics such as dimensional stability andmoisture-proof property, when compared with conventional biaxiallystretched polypropylene films. Thus, The biaxially stretchedpolypropylene film of the present invention has superior handlingconvenience and exhibits superior tension resistance against convertingtension applied during film converting such as printing, laminating,coating, metallization, and bag-making. The troubles derived from thequality of the base film, such as cracks and print pitch displacement,can be avoided. Moreover, since the film has a stiffness in thelongitudinal direction higher than that of the conventionalpolypropylene film of the same thickness and exhibits a superior tensionresistance, sufficient converting ability can be maintained with athickness smaller than that of conventional biaxially stretchedpolypropylene films.

[0486] The biaxially stretched polypropylene film of the presetinvention is suitable for packaging and for industrial use.

1. A biaxially stretched polypropylene film comprising a polypropylenewhich comprises a polypropylene having a melt strength (MS) and a meltflow rate (MFR) measured at 230° C. that satisfies formula (1) below:log(MS)>−0.61 log(MFR)+0.82   (1) and at least one additive that hascompatibility with the polypropylene and can provide plasticity duringstretching.
 2. A biaxially stretched polypropylene film comprising apolypropylene which consists of a polypropylene having a melt strength(MS) and a melt flow rate (MFR) measured at 230° C. that satisfiesformula (2) below: log(MS)>−0.61 log(MFR)+0.52   (2) and at least oneadditive that has compatibility with the polypropylene and can provideplasticity during stretching.
 3. A biaxially stretched polypropylenefilm according to claim 1 or 2, wherein the additive is a petroleumresin substantially containing no polar-group and/or a terpene resinsubstantially containing no polar-group.
 4. A biaxially stretchedpolypropylene film according to claim 1 or 2, wherein the polypropylenehas a meso pentad fraction (mmmm) in the range of 90 to 99.5%.
 5. Abiaxially stretched polypropylene film according to claim 1 or 2,wherein the Young's modulus in the longitudinal direction (Y(MD)) at 25°C. is at least 2.5 GPa.
 6. A biaxially stretched polypropylene filmaccording to claim 1 or 2, wherein the m value represented by theYoung's modulus in the longitudinal direction (Y(MD)) and the Young'smodulus in the transverse direction (Y(TD)) m=Y(MD)/(Y(MD)+Y(TD)) is inthe range of 0.4 to 0.7 at 25° C.
 7. A metallized biaxially stretchedpolypropylene film according to claim 1 or 2, a metallization layer isdeposited on at least one side.
 8. A metallized biaxially stretchedpolypropylene film according to claim 1 or 2, a coating layer comprisinga polyesterpolyurethane-based resin having a thickness of 0.05 to 2 μmand a metallization layer are sequentially formed on at least one side,wherein the adhesive strength between the base layer and the coatinglayer is at least 0.6 N/cm.
 9. A biaxially stretched polypropylene filmaccording to claim 1 or 2, wherein, in a 1-μm square area of a surfaceof the biaxially stretched polypropylene film, one side of the areabeing parallel to the longitudinal direction, at least one longitudinalfibril having a width of at least 40 nm and extending across two sidesparallel to the transverse direction is present.
 10. A biaxiallystretched polypropylene film comprising a polypropylene which comprisesa polypropylene having a Trouton ratio of at least 30 and at least oneadditive that has compatibility with the polypropylene and can provideplasticity during stretching.
 11. A biaxially stretched polypropylenefilm comprising a polypropylene which consists of a polypropylene havinga Trouton ratio of at least 16 and at least one additive that hascompatibility with the polypropylene and can provide plasticity duringstretching.
 12. A biaxially stretched polypropylene film according toclaim 10 or 11, wherein the additive is a petroleum resin substantiallycontaining no polar-group and/or a terpene resin substantiallycontaining no polar-group.
 13. A biaxially stretched polypropylene filmaccording to claim 10 or 11, wherein the polypropylene has a meso pentadfraction (mmmm) in the range of 90 to 99.5%.
 14. A biaxially stretchedpolypropylene film according to claim 10 or 11, wherein the Young'smodulus in the longitudinal direction (Y(MD)) at 25° C. is at least 2.5GPa.
 15. A biaxially stretched polypropylene film according to claim 10or 11, wherein the m value represented by the Young's modulus in thelongitudinal direction (Y(MD)) and the Young's modulus in the transversedirection (Y(TD)) m=Y(MD)/(Y(MD)+Y(TD)) is in the range of 0.4 to 0.7 at25° C.
 16. A metallized biaxially stretched polypropylene film accordingto claim 10 or 11, a metallization layer is deposited on at least oneside.
 17. A metallized biaxially stretched polypropylene film accordingto claim 10 or 11, a coating layer comprising apolyesterpolyurethane-based resin having a thickness of 0.05 to 2 μm anda metallization layer are sequentially formed on at least one side,wherein the adhesive strength between the base layer and the coatinglayer is at least 0.6 N/cm.
 18. A biaxially stretched polypropylene filmaccording to claim 10 or 11, wherein, in a 1-μm square area of a surfaceof the biaxially stretched polypropylene film, one side of the areabeing parallel to the longitudinal direction, at least one longitudinalfibril having a width of at least 40 nm and extending across two sidesparallel to the transverse direction is present.
 19. A biaxiallystretched polypropylene film, wherein, in a 1-μm square area of asurface of the biaxially stretched polypropylene film, one side of thearea being parallel to the longitudinal direction, at least onelongitudinal fibril having a width of at least 40 nm and extendingacross two sides parallel to the transverse direction is present.
 20. Abiaxially stretched polypropylene film according to claim 19, whereinthe Young's modulus in the longitudinal direction (Y(MD)) at 25° C. isat least 2.5 GPa.
 21. A biaxially stretched polypropylene film accordingto claim 19, wherein the m value represented by the Young's modulus inthe longitudinal direction (Y(MD)) and the Young's modulus in thetransverse direction (Y(TD)) m=Y(MD)/(Y(MD)+Y(TD)) is in the range of0.4 to 0.7 at 25° C.
 22. A biaxially stretched polypropylene filmaccording to claim 19, wherein the formula between the Young's modulusin the longitudinal direction (Y(MD)) at 25° C. and the heat shrinkingin the longitudinal direction (S(MD)) at 120° C. is satisfied:Y(MD)≧S(MD)−1
 23. A metallized biaxially stretched polypropylene filmaccording to claim 19, wherein a metallization layer is deposited on atleast one side.
 24. A metallized biaxially stretched polypropylene filmaccording to claim 19, wherein a coating layer comprising apolyesterpolyurethane-based resin having a thickness of 0.05 to 2 μm anda metallization layer are sequentially formed on at least one side,wherein the adhesive strength between the base layer and the coatinglayer is at least 0.6 N/cm.